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FLOWERS OF THE SKY 



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FLOWERS OF THE 
SKY 



By RICHARD Afl>ROCTOR 

AUTHOR OF "the EXPANSE OF HEAVEN," THE INFINITIES AROUND US,' 
"the UNIVfiRSE OF STARS," " THE SUN," " THE MOON," 
■^ ETC., ETC. 



WITH FIFTY' FOUR IIIUSTRATIONS 




A. C. ARMSTRONG AND SON 

714, BROADWAY 



All rights reserved 



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QBsi 

187? 



TRANSFBB 
O. 0, PUBLIC LIBBABir 
SEPT. lO, 1940 



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*' spirit of nature ! here, 
"In this interminable wilderness 
Of worlds, at whose immensity 
Even soaring fancy staggers, 
Here is thy fitting temple. 

Yet not the lightest leaf . 
That quivers to the passing breeze 
Is less instinct with thee." — Shelley. 



CONTENTS. 



PAGB 

I. LIGHT ,-,---- I 

II. SPACE - - - - - - 17 

III. THE INFINITELY MINUTE - - - - 31 

IV. THE MYSTERY OF GRAVITY - - - 43 

V. THE END OF MANY WORLDS - - " 5^ 

VI. THE AURORA BOREALIS - - - - 9I 

VII. THE LUNAR HALO - - - - - I r4 

VIII. MOONLIGHT - - - - - 125 

IX. THE PLANET MARS - - - - 149 

X. THE PLANET JUPITER - - - - I9I 

XI. THE RINGED PLANET SATURN - - - 21 5 

XII. FANCIED FIGURES AMONG THE STARS ^ - 236 

XIII. TRANSITS OF VENUS - - - -273 



\^ 



I. 

LIGHT, 

** Vriiat soul was his, when, from the naked top 
Of some bold headland, he beheld the smi 
Rise up and bathe the world in light ! He looked — 
Ocean and earth, the solid frame of earth 
And ocean's liquid mass, beneath him lay 
In gladness and deep joy.'' 

E live in a mighty ocean whose waves are 
ever rushing hither and thither, always 
according to law, with velocity inconceiv- 
able, almost immeasurable. These waves lave the shore 
of that island of space which is our home, travelling 
to it from remotest regions, and making known to us 
all that we know of what lies outside our small abode. 
We call these waves, or rather their effects, by the name 
of Light. We recognise in light — 

*' offspring of Heav'n's first-bom 
And of th' Eternal co-eternal beam '*— 

the antecedent of all else that exists in the universe ; 

I 




2 LIGHT. 

or^ as Sir John Herschel said, '^ the superior in point of 
rank and conception to all other products or results of 
creative power in the physical world. It is light which 
alone can give, and does give us, the assurance of a 
uniform and all-pervading energy — a mechanism almost 
beyond conception, complex, minute, and powerful, by 
which that influence, or rather that movement, is pro- 
pagated. Our evidence of the existence of gravitation 
fails us beyond the region of the double stars, or leaves 
at best only a presumption amounting to moral convic- 
tion in Its favour. But the argument for a unity of 
design and action afforded by light stands unweakened 
by distance, and is co-extensive with the universe itself" 

What, then, is light ? What is that mysterious move- 
ment of some essence pervading all space, whereby, 
from remotest depths, news is brought to us, after 
journeys lasting many years, though space is traversed 
at a rate exceeding more than ten million times the 
velocity of the swiftest express train? 

Light is in reality the result of undulations in what is 
called the ether of space, a perfectly transparent, almost 
perfectly elastic medium, occupying not only void space, 
but flowing as freely through the densest solids as the 
summer breeze flows through the forest trees. The 
waves of light cannot in this way pass through solid 
or liquid, or even aerial bodies, but either they are 



LIGHT, 3 

sooner or later brought to rest, or else they are more 
or less gradually deflected; just as the waves which 
traverse the ocean come to their end, or are deflected, 
when they meet the shore or shallows near the shore. 

All light, however, has its real origin, not in the 
ethereal ocean itself, but in the movements of the 
minute particles of which all forms of matter known to 
us are composed. A tiny atom, far too small to be per- 
ceived with a microscope, even though one should be 
made ten thousand times more powerful than any yet 
constructed, when set in rapid vibration, raises minute 
waves in the ethereal ocean, just as a small body, vibrat- 
ing on the surface of a sheet of water, would generate 
waves there. And as the water-waves would travel 
radially away from the place of their birth, so do the 
light-waves generated by the vibrations of one of the 
atoms composing a luminous body radiate forth in all 
directions through the ethereal ocean until, encountering 
some obstacle, they are sent (reduced in size) in a new 
direction. 

In some luminous bodies there are atoms vibrating 
in many different periods (all very small) so as to 
cause light-waves of many different kinds to proceed 
from the body. In other cases the atoms all vibrate 
at one rate, or at two or three or some definite num- 
ber of rates, so that only light-waves of certain kinds 



4 LlGIlT. 

proceed from the body. But in all cases these light- 
waves only cause us to see the body when they flow in 
through the pupil of the eye, and falling upon the retina 
(or the choroid membrane, or whatever part of the eye 
it may be which finally receives the waves), convey to 
the optic nerve, and thence to the brain, the information 
that such and such a body, so coloured, so shaped, so 
moving, exists towards that direction from which the 
light-waves seem to come. The body so seen, as we call 
it, may be the original source of light, or may be a body 
on which light has been reflected to us. 

It is in this way that we receive information from light- 
waves. It will be conceived how minute they must be, 
how perfectly they must retain their separate character, 
multitudinous though they are, in traversing the ether 
(even when that ether is clogged by the gross matter of 
our ordinary air), if we remember how through the tiny 
eye-pupil we often receive light-waves telling us of all the 
details, all the varieties of colour and brightness, all 
the movements in a rich landscape. 

Even more startling are the thoughts suggested by a 
view of the starlit heavens. From hundreds of suns at 
once the light-waves which have traversed varying but all 
enormous distances pour in upon the small circle of the 
eye-pupil, waves of many kinds coming in together from 
each sun. The waves which thus reach the eye from one 



LIGHT, 5 

bright star have been but a few years upon their journey; 
all that time they have been traversing an ocean swept 
in every part by untold millions of other waves, and yet 
they arrive as perfect in order and regularity as rollers 
which have traversed a wide sea pour in upon a level 
shore. From another star, as bright as the first, they 
have been years in travelling; from some among the 
fainter stars, hundreds, perhaps thousands of years. Yet 
still they flow on, each order of waves in perfect uni- 
formity as when they first left their parent sun. 

But even this is not all. Among the waves which reach 
the eye many, nay, most, are so small that ordinary vision 
cannot perceive their action. Take, however, a telescope, 
and so gather them together as to intensify this action, 
and they are rendered perceptible, just as the unnoticed 
heaving of ocean becomes a manifest wave-motion when 
it reaches a regularly narrowing inlet. Thus, from stars 
so remote that their light has required thousands, or, 
even in some cases, perhaps, hundreds of thousands 
of years in reaching us, the light-waves flow steadily 
in upon us. So small are these waves, that the breadth 
of from forty to sixty thousand of them would occupy but 
a single inch. Through every point in space waves from 
all the hundred millions of stars are at all times simul- 
taneously rushing at the rate of one hundred and eighty- 
five thousand miles in every second of time : yet they 



6 LIGHT. 

travel on altogether undisturbed, and each tells its story 
as distinctly as though the ether had conveyed no other 
message, and that message but for a short distance. 

It would be difficult to say which thought, considered 
in its real significance, is more striking, — the thought of 
what is done for us by light regarded as a terrestrial phe- 
nomenon, or the thought of what light is doing, and has 
done, in presenting to us a view of the starlit heavens. 

When the sun rises in splendour above the eastern 
horizon, tinting the sky with varied colours, lighting up 
the clouds which till then have been but dark patches on 
the heavens, bringing out the colours of hill and dale, 
rock and river, fields and woods, the heart gladdens at 
the spectacle. A pleasing melancholy falls on us as the 
light fades away at eventide, tint after tint vanishing, 
until 'at length the gloom of night enshrouds alL The 
full splendour of mid-day, the chastened splendour of a 
moonlit night, and the glory of the heavens when "all 
the stars shine, and the shepherd gladdens in his heart," 
stir the soul in like manner ; and it might seem to many 
that to analyse these glories, to explain their scientific 
meaning, would be to rob the mind of the pleasure it 
had before found in such scenes. Many would be dis- 
posed to think that a purer enjoyment is expressed by 
Augustine than, any student of science could find in the 
wonders of light, in those words in which he expresses 



1 



LIGHT. 9 

his sense of the loveliness of fair forms and brilliant 
colours. '' For light, queen of the colours," he says, 
'' bathing all I can look upon, from morning till evening, 
let me go where I will, will still keep gliding by me in 
unnumbered guises, and soothe me whilst I am busy at 
other things, and am thinking nothing of her.'' But the 
sensuous pleasure afforded by light is enhanced, while a 
purer and higher enjoyment is superadded, when the real 
meaning of the display is understood. As the astronomer 
sees in the sun a more glorious object than the sun of 
the poet, recognising in imagination not only the visible 
splendour of that orb, but the mighty energy with which 
it is swaying the motions of a scheme of circHng w^orlds, 
the wondrous activities at work throughout its entire 
frame, the inconceivable tumult which must prevail in 
that seemingly silent globe, so the glories of light, rightly 
understood, are far more impressive than as they appeal 
simply to the senses. 

<ronsider, for instance, the real meaning of sunrise. 
The orb seemingly rising above the horizon, but, in 
reality, at rest, is the source of all the glory which is 
spreading over the fair face of earth. The atoms of that 
remote body, vibrating with intensest activity, send forth 
in all directions ethereal waves, and of these relatively 
but a very few, about one in two thousand millions, fall 
upon our earth, producing the phenomena of sunlight. 



lo LIGHT, 

They have been little more than eight minutes on the 
road, but in that short time they have traversed more 
than 90,000,000 of miles. Were they to fall directly 
upon our earth, we should see few of the splendours 
which attend the uprising of the sun. The deep air 
clothing our earth receives the onward rushing waves, 
and reflects them in all directions. To use Biot's simile, 
" The air is a sort of briUiant veil, which multiplies and 
diversifies the sunlight by an infinity of repercussions." 
Nor is the wonder of the scene, or its effect in filling the 
mind with solemn and poetic thoughts, diminished — 
on the contrary, it is enhanced — by the recollection 
that the gradually growing glory of day is brought about 
by the slow turning of the mighty earth, — 

* * that spinning sleeps 
On her soft axle, as she paces even, 
And bears us soft with the smooth air along." 

But if this is true of a scene of terrestrial splendour, 
how much more fully may it be said of the glories of the 
heavens? No poet, if unaware of the real meaning of 
modern discoveries respecting the celestial bodies, can 
be moved by the starlit depths as the astronomer is, at 
least the astronomer whose study of science is not limited 
to mere observation and calculation. Hundreds of 
bright points of light sparkling, and sometimes varying 
strangely in colour, form, no doubt, a beautiful scene \ 



LIGHT, II 

but the scene is not less beautiful, and certainly it is far 
more impressive, when we remember that every one of 
these points of light is a sun, mighty in attractive energy 
like ours, its whole surface glowing with fiery heat, and 
every particle of its substance constantly in motion, if 
not always in the fierce rush of cosmic hurricanes, yet 
with the ceaseless vibrations which generate the ethereal 
light-waves telling us of the star's existence. 

There is one strange thought connected with the 
motion of light-waves through the ether of space which 
has not, I think, received the attention it deserves. 

Every one knows that when we look at the heavens we 
do not see the celestial bodies where they are, but where 
they were^ and again, not where they were at any one 
moment of time, but some where they were a short time 
ago, others where they were very long ago. But it is 
not so generally known, or remembered by those who do 
know it, that if light were not so active as it is the result 
would be that utterly incorrect pictures of the celestial 
depths would continually be presented to us. As matters 
actually are no orb in space can appear very far from its 
true place. We see the sun, for instance, at any moment, 
not where he is, but w^here he w^as (or rather towards the 
direction in which he lay) about eight minutes before. 
But as the real velocity of the earth, and therefore the 
apparent velocity of the sun, amounts only to about 



12 LIGHT, 

eighteen miles per second, the sun is only thrown about 
9000 miles out of his true position, which is but about 
the ninetieth part of his diameter : so that we see the sun 
very nearly in his right place. Now it might seem that 
a star whose light takes, say, twenty years in reaching us, 
must be seen very far from its true place, supposing the 
star to be travelling along very quickly j and, in one 
sense, this is true. If such a star is moving at the rate 
of fifty miles per second, athwart the Hne of sight, it 
will be out of place by so considerable a distance as 
315,000,000,000 of miles. Yet the star will appear very 
nearly in its true position, simply because, at the star's 
enormous distance from us, even the great distance just 
named is reduced to a very small apparent amount. 
Such a star w^ould, in fact, be displaced by only about 
the thirtieth part of the sun's or moon's apparent diame- 
ters, or by about a fifteenth part of the distance separat- 
ing the middle star of the Great Bear's tail from its 
small companion, sometimes called Jack by the Middle 
Horse. Thus the stellar heavens present very truly to us 
the positions of the stars; for such athwart motion as I 
have just imagined would be very much larger than the 
motion of far the greater number of the stars. But we 
only thus see the heavens truly pictured because of the 
enormous velocity with which light travels. If light 
swept along only at the rate of a hundred miles in a 




!!illil!!lilii!!ll!illl!ii!i||!i 



m 




LIGHT. 15 

second (a velocity still far beyond our powers of concep- 
tion), there would be no believing what we should see, 
for every star, and our own sun, and all the planets, and 
even our o^vn companion planet, the moon, would be 
thrown in appearance very far from their true positions. 
If they were all shifted in position by the same amount 
and in the same direction the picture would still be true, 
in a sense, just as we see a true picture of an object at 
the bottom of a clear lake, though the picture is dis- 
placed by the refractive action of the water on the 
rays of light. But, in the imagined case, the sun, 
and moon, and planets, and stars would be shifted 
by different amounts and in different ways, simply 
because they are moving at different rates and in 
different directions. The scene presented to us would 
have been utterly untrue. Astronomy as a science 
could probably have had no existence in such a case. 
Assuredly it could have had no existence until students 
of the heavenly bodies had learned to accept as the 
first axiom of their science the doctrine that ^^ Seeing 
is not believing." 

A strange thought truly, that so active are the orbs 
peopling space, so s\viftly do they rush onwards upon 
their orbits, that light, carrying its message at a rate 
exceeding six thousand times the velocity of the swiftest 
express train, woiild be utterly unable to give a true 



16 LIGHT, 

account of the position and movements of the celestial 
bodies. Fortunately light gives a true record, because 
the qualities of the cosmic ether are such that the mes- 
sage of light is transmitted hundreds of times more 
swiftly than the swiftest bodies in the universe travel 
onwards upon their orbits around each other or in 
space. 




11. 

SPACE 

^LTHOUGH astronomy tells us in clearest 
words of the vast depths of space which 
surround our earth on all sides, we are not 
thereby enabled to realize their enormous extension. It 
is not merely that the unknown depths beyond the range 
of our most powerful telescopes are inconceivable, but 
that the parts of space which we can examine are on too 
large a scale for us to conceive their real dimensions. 
It is hardly going too far to say that our powers of 
actual conception are limited to the extent of space 
over which the eye seems to range in the daytime. Of 
course in the daytime, at least in clear weather, there 
is one direction in which the eyesight ranges over a 
distance of many millions of miles, — namely, where we 
see the sun. But the sense of sight is not cognisant of 
that enormous distance, and simply presents the sun to 



1 8 SPACE. 

US as a bright disc in the sky, or perhaps rather nearer to 
us than the sky. Even the distance of the sky itself is 
under-estimated. A portion of the Ught we receive from 
the sky on a clear day comes from parts of the atmos- 
phere distant more than thirty or forty miles from us ; 
but the eye does not recognise the fact. The blue sky 
seems a little farther off than the clouds, but not much ; 
the light clouds of summer seem a little but not much 
farther off than the heavier clouds of a mnter sky; a 
cloud-covered winter sky seems a little farther off than 
heavy rain-clouds. The actual varieties of distance 
among clouds of various kinds are not much more 
clearly discerned than the actual varieties of distance 
among the heavenly bodies. The estimate formed of 
the distance of a cloud-covered sky overhead probably 
amounts to little more than a mile, and it is very doubt- 
ful whether the mind presents the remotest depths of a 
blue sky overhead at more than two miles. Towards 
the horizon the distance seems greater, and probably on 
a cloudy day the sky near the horizon is unconsciously 
regarded as at a distance of about five miles, while 
blue sky near the horizon may be regarded as lying at a 
distance of six or seven miles, the arch of a blue sky 
seeming to be far more deeply curved than that of a 
cloud-covered sky. 

It is to distances such as these that the mind uncon- 



SPACE. 19 

sciously refers the celestial bodies. We know that the 
moon is about 2,000 miles in diameter, but the mind 
refuses to present her to us as other than a round 
disc much smaller than those other objects in sight 
which occupy a much larger portion of the field of 
vision. The sun cannot be conceived to exceed the 
moon enormously in size, seeing that he appears no 
larger; and all the multitude of stars are judged by 
the sight to be mere bright points of light in reaUty as 
they appear to be. 

How, then, can we hope to appreciate the vastness of 
space whereof astronomy tells us ? To the student of 
science attempting to conceive the immensities of whose 
existence he is assured, the same lesson might be taught 
in parable which the child of St. Augustine's vision 
taught the Numidian theologian. As reasonably might 
an infant hope to pour the waters of ocean into a hollow, 
scooped with his tiny fingers in the sand, as man to 
picture in his narrow mind the length and breadth and 
depth of the abysses of space in which our earth is lost. 

Yet, as a picture of a great mansion may be so drawn 
on a small scrap of paper as to convey just ideas of its 
proportions, so may the great truths which astronomy 
has taught us about the depths of space be so presented 
that just conceptions may be formed of the proportions 
of at least those parts of the universe which lie within 



20 SPACE. 

the range of scientific vision, though it would be hopeless 
to attempt to conceive their real dimensions. 

Thus, when we learn that a globe as large as our 
earth, suspended beside the moon, would seem to have a 
diameter exceeding hers nearly four times, so that the 
globe wo uld cover a space in the heavens about thirteen 
times as large as the moon covers, we form a just con- 
ception of the size of the moon as compared with the earth, 
though tlie mind cannot conceive such a body as the 
moon or the earth really is. When, in turn, we are told 
that if a globe as large as the earth, but glowing as brightly 
as the sun, were set beside the sun, it would look a mere 
point of light, we not only learn to picture rightly to our- 
selves how largely the sun exceeds the earth, but also 
how enormous must be the real distance of the sun. 

Another step leads us to a standpoint whence we can 
form a correct estimate of the vast' distance of the fixed 
stars j for we learn that so enormous is the distance of 
even the nearest fixed star, that the tremendous space 
separating the earth from that star sinks in turn into the 
merest point, insomuch that if a globe as bright as the 
sun had the earth's orbit as a close fitting girdle, then 
this glorious orb (with a diameter of some 184,000,000 
of miles) would look very much smaller than such a 
globe as our earth would look at the sun's distance — 
would, in factj occupy but about one-fortieth part of the 



SPACE. 21 

Space in the sky which she, though she would then look 
a mere point, would occupy if viewed from that distance. 

But there is a way of viev/ing the immensities of space 
which, though not aiding us indeed to conceive them, 
enables the mind to picture their proportions better than 
any other. The dimensions of the earth's path around 
the sun sink into insignificance beside those of the 
outermost planets ; but these in their turn dwindle into 
nothingness beside those of some among the comets. 
From the paths of these comets, if only sentient and 
reasoning beings could trace out in a comet's company 
those mighty orbits, and could have for the duration 
of their existence not the brief span of time which 
measures the longest human life, but many circuits of 
their comet home around the same ruling orb (as 
we live during many circuits of our globe around the 
sun), the dimensions of the star-depths, which even to 
scientific insight are all but immeasurable, would be 
directly discernible. Not only would the proportions 
of that mighty system be perceived, whose fruits and 
blossoms are suns and worlds, but even the gradually 
changing arrangement of its parts could be discerned. 

Some comets, indeed, as I pointed out in an essay on 
comets several months ago (see Expanse of Heaven, 
p. 149), do not travel around the sun, but flit from 
sun to sun on journeys lasting millions of years, paying 



22 SPACE. 

each sun^ but a single visit. A being inhabiting such 
a comet, and having these interstellar journeys as the 
years of his existence, so, that he could live through 
many of them, would have a wonderful insight into the 
economy of the stellar system. If his powers of con- 
ception as far exceeded ours as the range of his travels 
and the duration of his existence, he would be able to 
recognise the proportions of a large part of the stellar 
universe as clearly as we recognise the proportions of 
the solar system. 

But leaving these wonderful wanderers, whose journeys 
are as far beyond our powers of conception as the im- 
mensity of the regions of star-strewn space^ we may find, 
among the comets belonging to the sun's domain, bodies 
whose range ot travel would give their inhabitants far 
clearer views of the architecture of the heavens than 
even the profoundest terrestrial astronomer can possibly 
obtain. 

Such a comet as Halley's (fig. 3) for instance, though 
one of comparatively limited range in space, yet travels so 
far from the sun that, from the extreme part of its path, 
it sees the stars displaced nearly twenty times as much 
(owing to its own change of position) as they are from 
the earth on opposite sides of her comparatively narrow 
orbit. And the length of this comet's year, if it indi- 
cated the length of the lives of all creatures travelling 



r 



SPACE. 



23 



along with it, would suggest a power of patiently watch- 
ing the progi^ess of changes lasting not a few of our 
years only, but for cen- 
turies. Seventy-five or 
seventy-six years elapse 
between each return of 
this comet to the sun's 
neighbourhood, and 
one who should have 
lived during sixty or 
seventy circuits of this 
body around its mighty 
orbit would have been 
able to watch the rush 
of stars, with their ve- 
locities of many miles 
per second, until visible 

displacements had Fig. 3— Halley's Comet of 1835. 

taken place in their positions. 

This, however, is as nothing compared with the 
mighty range in space and the enormous period of the 
orbit of the great comet of the year 181 1 (fig. 4). This 
comet is, on the whole, the most remarkable ever known. 
It was visible for nearly seventeen months, and though 
it did not approach the sun within 100,000,000 miles, 
and was therefore not subject to that violence of action 




24 SPACE, 

which has caused enormous tails to be thrown out from 
Comets which have come within a few million miles 
of him, or even within less than a quarter of his own 
diameter, it flourished forth a tail 120,000,000 of miles 
in length. Its orbit has, according to the calculations of 
the astronomer Argelander, a space exceeding the earth's 
distance from the sun 211 times, and thus surpassing 
even the mighty distance of Neptune fully seven times. 
It occupies in circuiting this mighty path no less than 
3065 of our years (with a possible error either way of 
about forty-three years). So that, according to Bible 
chronology, this comet's last appearance probably oc- 
curred during the rule of the judge Tola, son of Puah, 
son of Dodo, over the children of Israel, though it may 
have occurred during the rule of his predecessor Abime- 
lech, or during that of his successor Jair.'^' During 
one half of the enormous interval between that time 
and 181 1 the comet was rushing outwards into space, 

* It might be suggested that the appearance of this blazing comet 
among the stars drove the more superstitious of the Israelites at that 
time to the worship of star-gods, as we read how, during the judg- 
ship of Jair, they ** served Baalim, and Ashtaroth, and the gods of 
Syria, and the gods of Moab, and the gods of the Philistines, and 
forsook the Lord and served not Him.'* To a people like the Jews, 
who seem to have been in continual danger of returning to the 
Sabaistic worship of their Chaldean ancestors, the appearance of a 
blazing comet may have been a frequent occasion of backsliding. 



1^ 




Fig. 4.— Comet of iSit. 



SPACE. £7 

reaching the remotest part of its path somewhere about 
the year 278 (a.d.), and from that time to i8ri it was on 
its return journey. It is strange to think, however, that 
though the remotest part of its path lay 211 times farther 
from the sun than the earth's orbit, yet even this mighty 
path, requiring more than 3000 years for a single circuit, 
cannot be said to have carried the comet into the star- 
depths. If the earth were to shift its position by the 
same enormous amount the nearest fixed star would have 
its apparent position changed only by about an eighth 
part of the apparent diameter of the sun or moon, or by 
about one-quarter of the distance separating the middle 
star of the Bear's tail from its close companion. 

But this fact of itself is most strikingly suggestive of 
the vast distance of the stars. For consider what it 
means. Imagine the middle star of the Bear's tail to be 
the really nearest of all the stars instead of lying probably 
twenty or thirty times farther away. Conceive a comet 
belonging to that sun after making its nearest approach 
to it to travel away upon an orbit requiring 3000 years for 
each circuit. Then (supposing that star equal to our sun 
in mass), the comet, though rushing away from its sun 
^\ith inconceivable velocity during 1500 years, would, at 
the end of that vast period, seem to be no farther away 
than one-fourth of the distance separating the sun from its 
near companion. Look at the middle star of the Bear's 



28 



SPACE. 



tail on any clear night, and on its small satellite, remem- 
bering this fact, and the awful immensity of the star 
depths are strongly impressed upon the mind. But the 
observer must not fail to remember that the star really 
is many times more remote than we have here for a 




Fig. 5— Six-tailed Comet of 1744. 



moment supposed, and that such a comet's range of 
travel would be proportionately reduced. Moreover, 
many among the stars are, doubtless, hundreds, even 
thousands, of times still farther away. 
Let us turn lastly to the amazing comet of the year 



SPACE. 29 

1744, pictured, at the time, as shown in fig. 5 (though 
probably the drawing is greatly exaggerated). We find 
that though it had the longest period of any which 
has ever been assigned to a comet as the result of actual 
mathematical calculation, yet its range in space would 
scarcely suffice to change the position of the stars in 
such sort that the aspect of the familiar constellations 
would be materially altered. Euler, the eminent mathe- 
matician, calculated for this comet a period of 122,683 
years, which would correspond, I find, to a distance of 
recession equal to 2469 times the distance of the earth 
from the sun, or about eighty times the distance of 
Neptune, Yet this is but little more than twelve timcJ 
the greatest distance of the comet of 181 1. Probably 
the actual range of such an orbit from the middle star of 
the Bear's tail would be equal in appearance to the range 
described above on the supposition that the star is no 
farther from us than the nearest known star (Alpha 
Centauri). That is, such a comet, if it could be seen 
and watched during a period of about 122,000 years, 
would seem to recede from the star to a distance equal to 
about one-fourth the space separating it from its close 
companion, and then to return to the point of nearest 
approach to its ruling sun. 

Such are the immensities of star-strewn space ! The 
journey of a comet receding from the sun with incon- 



30 SPACE, 

ceivable velocity during hundreds of thousands of years 
carries it but so small a distance from him compared 
with the distance of the nearest star as scarcely to change 
the appearance of the celestial landscape ; and yet the 
distances separating the sun from the nearest of his 
fellow suns are but as hair-breadths to leagues when 
compared with the proportions of the scheme of suns to 
which he belongs. These distances, though so mighty 
that by comparison with them the inconceivable dimen- 
sions of our own earth sink into utter nothingness, do 
not bring us even to the threshold of the outermost 
court of that region of space to which the scrutiny of 
our telescopes extends. Yet the whole of that region is 
but an atom in the infinity of space. 



III. 



CF THE INFINITELY MINUTE. 




\ HEN I speak of the infinitely minute, I use 
the word infinitely not in its absolute sense, 
but relatively. Actual infinity of minute- 
ness is as utterly beyond our conceptions as actual 
infinity of vastness. But we may speak of what is very 
much less than the least object of which our senses can 
make us directly conscious as for us infinitely minute. 
Among the greatest wonders science has to deal with are 
those relating to bodies and movements thus beyond the 
direct ken of our senses. There is a universe within the 
universe which our senses reveal to us, — a universe whose 
structure is so fine that the minutest particle which the 
microscope can reveal to us is, by comparison, like one 
of the suns which people our universe compared with 
the unseen particles constituting matter. 

It is a strange thought that the objects constituting 



32 OF THE INFINITELY MINUTE. 

our universe, so long regarded by man as the only uni- 
verse, are in a sense pervaded by the materials of an 
utterly different universe, — which yet is as essential to 
our very existence as what we commonly call matter. 
Wc cannot live without light and heat, for instance, and 
again, light and heat affect matter as we know it; but 
they thus exist and affect such matter by means only of 
a form of matter unlike any which we can conceive. 
It is certain tliat if absolute vacancy separated our earth 
from the sun, even by the narrowest imaginable gap, his 
heat and light could never reach us. They could on 
more pass that vacant space than tlic wave-motion of 
water can cross a space where water itself is wanting. 
It is because of relations such as these that it has been 
said, and justly, that matter is the less important half 
of the material constituting the physical universe. 

Our knowledge of this universe within our universe 
has been obtained within comparatively recent years. 
Men were unwilling or at least they spoke and thought 
as if they were unwilling, to believe that the universe 
of matter which they had so long recognised was de- 
pendent on another universe for its chief if not all its 
properties. They regarded heat as some sort of sub- 
stance, which might, with more delicate means than they 
possessed, admit of being dealt with as chemists had 
dealt with the gases. The sun was full of this fluid, this 



OF THE INFINITELY MINUTE. 33 

phlogiston, as it was called. Light, in so far as it could 
be distinguished from heat, was another fluid ; electri- 
city was another. These were the imponderables, or un- 
weighable substances of last century's science, — not as 
with us, the effects of modes of motion taking place in a 
universe which, though material, is yet not made of 
matter such as we know, or even such as we can at 
present conceive. 

This is the greatest of all human scientific marvels, — ■ 
the greatest because it includes all others. We know of 
a universe which is as infinite in extent, and doubtless in 
duration, as our own universe ; which pervades all forms 
of matter : and yet we know of this universe only in- 
directly ; by the effects of movements taking place within 
it, not by any perception of these movements themselves. 
Waves are ever beating upon the shores of our material 
universe, and constantly changing the form and condition 
of the coast line, but the waves themselves are unseen. 
We only know of their existence through the changes 
wrought by them. 

We speak of the ether of space, and of waves travers- 
ing it, as though the ether were simply some fluid very 
much more attenuated than the rarest gas, even in a so- 
called vacuum. But in reaUty, so soon as we attempt to 
apply to the movements taking place in such an ether 
the mechanical considerations which ^ufifice for the 

3 



34 OF THE INFINITELY MINUTE, 

motions of all ordinary forms of matter, we perceive that 
it must of necessity be utterly unlike any kind of sub- 
stance known to us. For instance, we find that though 
it is like a gas in being elastic, its elasticity is infinite 
compared with that of any material gas. Again, it is like 
a solid in retaining each of its particles always very near 
to a fixed position ; but again, no solid we know of 
can be compared with it for a moment as respects this 
kind of rigidity. It is at once infinitely elastic and 
infinitely rigid. We cannot, for example, explain the 
phenomena of light unless we suppose the elasticity of 
the ether at least 800,000,000,000 times greater than 
the elasticity of air at the sea-level ; and yet, as Sir J. 
Herschel long since pointed out, every phenomenon of 
light points strongly to the conclusion that none of the 
particles of the ether can be " supposed capable of inter- 
changing places, or of bodily transfer to any measurable 
distance from their own special and assigned localities 
in the universe. Again, how are we to explain the con- 
tinuance of the ether in its present condition, when we 
recognise the fact that a gas of similar elastic power 
would expand in all directions with irresistible force, 
diminishing correspondingly in density ; yet the ether of 
space remains always, so far as we can judge, absolutely 
unchanged in position. Its characteristics certainly re- 
mained unchanged. Light travels at the same rate now 



OF THE INFINITELY MINUTE. 35 

as it did last year, last century, a million years ago. The 
ether, then, that bears it has presumably remained un- 
changed. If it were gaseous, and bounded on all sides 
by vacuum, it would expand with inconceivable velocity. 
To suppose it infinite in extent is to get rid of the diffi- 
culty perfectly ; but only by introducing a difficulty far 
greater."'* 

A wonderful feature of the infinitely tenuous ether 
is, that while its ultimate particles must be inconceiv- 
ably more minute than the ultimate atoms of ordinary 
matter, the movements taking place in it are trans- 
mitted with enormous velocities. The structure of our 
universe is on a grander scale ; its least atom may com- 
prise millions of millions of the largest component 

* I do not say we can in any way avoid this far greater difficulty. 
Our own material universe cannot even be conceived as limited in 
any way save by void space of infinite extent ; and it is as impossible 
for us to conceive an infinite void as to conceive the infinite exten- 
sion of matter. Some modern mathematicians, indeed, assert that 
space is not necessarily infinite, but they accompany the assertion 
(very justly) with the admission that we cannot possibly conceive any 
boundary to space ; and as one of the things they ask mathematicians 
to admit is the possibility that a straight line indefinitely produced 
both ways will at length re-enter into itself, while another is the 
possibility that in other parts of the universe two and two may 
make three or five, they are not likely, I conceive, to persuade most 
mathematicians (profoundly mathematical though they are them- 
selves) that the mystery of infinity has been as yet entirely ex- 
pounded. 



36 OF THE INFINITEL V MINUTE, 

portions of that infinitely tenuous ether. But amid 
that ether motions arc transmitted with velocities trans- 
cending all but infinitely those which take place among 
the particles of matter composing the universe in which 
we ^^ live and move and have our being." The planets, 
immense aggregates of matter such as we know it, 
sweep onwards upon their immense orbits, traversing 
many thousands of miles in an hour; but light and 
heat sweep along the ether of space, and by virtue of 
motions taking place within that ether at the rate of 
many tens of thousands of miles per second. The 
suns which people space rush onwards with mightier 
momentum, but less swiftly than the planets in their 
orbits. Comets attain the greatest velocities of all the 
bodies that science deals with, rushing sometimes, in 
their periastral swoop, with a velocity of hundreds of 
miles per second, — though yet in mid-space the comets 
of widest orbital range lag slowly enough, insomuch 
that some of those which, when nearest our sun, travel 
at the rate of two or three hundred miles per second, 
move more slowly when very far from him than many 
of our rivers. Taking even the swiftest rush of a 
comet within the solar domain, we find that light speeds 
along five hundred times more quickly, — so that if we 
represent the velocity of light by that of an express 
train (reducing light's velocity in scale to ^bout 



OF THE INFIMTELV MEVUTE, 37 

one-io,ooo,oooth part of its real value), the velocity of 
the most swiftly-moving comet would be represented 
by that of a walk at the rate of one-eighth of a mile 
per hour, — a very slow walk indeed. 

It is not only amid the depths of space that these 
wonderfully swift motions take place in the ethereal 
universe. As I have said, that universe pervades ours 
throughout its entire extent. The densest of our 
solids is as freely traversed by the ether as a forest by 
the summer breeze. As the foliage of a thick forest 
may prevent the passage of fierce winds, so may a solid 
body prevent the passage of light-waves — though all 
solid bodies, as we know, do not prevent, and some 
scarcely even modify, the passage of light. But sub- 
stances which prevent the passage of light are yet 
found capable of transmitting ethereal motions of 
similar velocity. According to Wheatstone's experi- 
ments electricity travels at the rate of more than 
200,000 miles per second along stout copper wire. 
Fizeau's experiments gave a lower speed ; but they did 
not negative Wheiatstone's, the conditions not being the 
same. Can anything be more wonderful than the 
thought of the transmission of electricity with this enor- 
mous velocity? What really happens we do not know. 
Perhaps if we were told what really takes place be- 
tween and among the particles of the wire, we should 



38 OF THE INFINITEL V MINUTE. 

find ourselves utterly unable to conceive it — for, as 
we have seen, the properties of the ether, and, there- 
fore, the processes taking place in the ethereal universe, 
are probably unlike any within our experience. But 
this w^e know — a certain condition of the molecules of 
the wire is transmitted, by virtue of the ethereal medium 
pervading the wire, at a rate so enormous that, if the 
wire itself could move at that rate, the force required 
to bring its mass to rest would suffice to generate 
enough heat to turn many times as much metal into 
the vaporous state. 

Nay, even as regards the energy of their action on the 
matter of our universe, these movements in the ethereal 
universe enormously exceed the forces we are accus- 
tomed to regard as most powerful. The effects pro- 
duced by gravity, for instance, are almost evanescent 
compared with those produced by heat. The sun's 
rays poured on a piece of metal for a few minutes pro- 
duce motions in every one of the ultimate particles of 
the metal. Each particle vibrates with inconceivable 
rapidity (referring to the rate at which the vibrations 
succeed each other), and with great actual velocity of 
motion. Summing up the energy thus pervading the 
piece of metal, we find that it incalculably exceeds the 
energy represented by the velocity which the sun's 
attraction would communicate in the same interval to 



OF THE INFINITELY MINUTE, 39 

that piece of metal, supposed to be entirely under its 
influence at the earth's distance from the sun. 

Or take another instance. "Think for a moment," 
say the authors of the " Unseen Universe/' " of the 
fundamental experiments in electricity and magnetism, 
known to men for far more than 2000 years, — the lift- 
ing of light bodies in general by rubbed amber and 
of iron filings by a loadstone. To produce the same 
effect by gravitation-attraction, — at least, if the attract- 
ing body had the moderate dimensions of a hand- 
specimen of amber or loadstone, — we should require it 
to be of so dense a material as to weigh, at the very 
least, 1,000,000,000 pounds, instead of (as usual) a 
mere fraction of a pound. Hence it is at once 
obvious that the imposing nature of the force of 
gravity, as usually compared with other attractive 
forces, is due, not to its superior qualitative magni- 
tude, but to the enormous masses of the bodies which 
exercise it.'' 

We may put this illustration in another form. When 
we place a powerful magnet near a piece of iron, say at 
a distance of one inch, and the magnet lifts that piece 
of iron by virtue of its attractive power, a contest has been 
waged, if one may so speak, between the attractive 
powers of the small magnet and of the mighty earth, 
and the magnet has conquered the earth. Now the 



43 OF THE INFINITE L Y MINUTE. 

magnet has been much nearer than the earth to the 
piece of iron, for we know that the earth's attractive 
influence has been the same as though the entire mass 
of the earth were gathered at its centre, say 4000 miles 
from the piece of iron. A distance of 4000 miles con- 
tains 4000 times 1760 times thirty-six inches, or, roughly, 
250 millions of inches. (This is in truth very near 
the true number of inches in the earth's radius, inso- 
much that many suppose the inch to have been ori- 
ginally taken as the 500,000,000th part of the earth's 
diameter. A British inch is about one-5oo,ooo,oooth 
part of the polar diameter of the earth.) Since attraction 
diminishes as the square of the distances increases, and 
vice versa, it follows that if the earth's entire mass could 
act on the piece of iron, at a distance of one inch, the 
attraction would exceed that actually exerted by the 
earth 250 million times 250 million times, or 62,500 
milHons of milHons of times. In this degree, then, the 
earth is at a disadvantage compared with the magnet 
as respects distance. And one-62, 500,000,000,000,000th 
part of the earth's mass would be capable of attracting 
the piece of iron as strongly as the earth actually 
attracts it, if that fraction of the earth's mass could 
exert its pull from a distance of only one inch. But a 
62,500,000,000,000,000th part of the earth would be 
an enormous mass. It v/ould weigh about 97,500 tons. 



OP THE INFINITELY MINUTE. 41 

or some 218 millions of pounds. Thus a magnet 
which a child can lift exerts a greater attraction on 
the piece of iron at the same distance than a mass at 
least 1000 million times its weight could ex^rt by its 
gravity only. 

In fact we see from this illustration that gravity, 
though it produces effects so tremendous, though it 
sways the moon round the earth, the earth and all 
the other planets around the sun, and urges the sun 
and his fellow- suns through space, is, after all, but a 
puny force in itself A child can lift his own weight 
against the attraction of the mighty earth ; and by 
combined strength as many children as would have a 
weight equal to the earth's would easily bear a weight 
exceeding the earth's, if the force could be wholly and 
directly applied to such work.^ 

The attraction of gravity must, however, be regarded 

* Of course the reader will understand that when I here speak 
of the earth's weight, I mean simply the pressure which would be 
exerted by the quantity of matter contained in the earth, if each 
portion were only subjected to an attractive force equal to that of 
gravity at the earth's surface. The actual force with which the 
earth is drawn in any direction, as a weight at the earth's surface 
is drawn downwards, depends on the distance and mass of the 
attracting body as well as on the mass of the earth ; and strictly 
speaking, we ought not to say that the earth weighs so many 
millions of tons, but that she contains so many million times as 
much matter as a mass which at her surface weighs a ton. 



42 OF THE INFINITELY MINUTE. 

as only one manifestation of the energies of the in- 
finitely minute. It is in this sense well worthy of 
careful study. I propose to present in a future paper 
some of the strange thoughts which are suggested by 
the action of this wonderful force, the range of whose 
activity is seemingly co-extensive with the material 
universe. 



IV. 



THE MYSTERY OF GRAVITY. 




'^HE law of gravity, or of the mutual attrac- 
tion of masses of matter upon each other, 
accounts so perfectly for all the observed 
motions of the heavenly bodies, that we are apt to 
regard Newton's discovery of the great law as though 
it had finally solved the mystery of these motions. 
Many accept the verdict given by the poet Pope in the 
famous epitaph which he suggested for Newton, — 

** Nature and Nature's laws lay hid in night : 
God said, Let Newton he I and all was Light.'' 

But Newton, who probably knew as much about his 
work as Pope, was of another opinion. Every one 
knows how he compared himself to a child who had 
picked up a few shells on the shore, while the ocean 
of truth lay unexplored before him. He has, however, 
spoken definitely of the great discovery which has 



44 THE MYSTERY OF GRAVITY, 

rendered his name illustrious, in terms which show that 
he did not find that all was light. Among the questions 
which he specially would have had answered, amongst 
the secrets of nature concealed beneath the ocean of 
truth, the mystery of gravity was probably the chief. 
When Newton asked of the Ocean of Truth what Mrs. 
Hemans later said, and in another sense, of the natural 
sea — 

*' What hidest thou in thy treasure-caves and cells, 
Thou hollow-sounding and mysterious main ? " 

he had in his thoughts the very power w^hich he is 
commonly supposed to have explained, but which was 
in truth for him, more than for any man that had ever 
lived, the mystery of mysteries. 

It may be well to consider the very words of the great 
pliilosopher, so far at least as our more diffuse language 
can present the concise expressions of the original Latin: 

*^ Hitherto we have explained," he says, "the pheno- 
mena of the heavens and of our sea by the power of 
gravity, but have not yet assigned the cause of this 
power. This is certain " (we must hearken attentively 
here, for when a man like Newton speaks of aught as 
certain, we have sure ground to go upon), — " this is cer- 
tain, that it must proceed from a cause that penetrates 
to the very centres of the sun and planets, without suffer- 
ing the least diminution of its forces ; that operates, not 



THE MYSTERY OF GRAVITY, 45 

according to the quantity of surfaces of particles on 
which it acts (as mechanical causes usually do), but 
according to the quantity of the solid matter which they 
contain, and propagates its virtue on all sides to immense 
distances, decreasing always as the squares of the dis- 
tances. Gravitation towards the sun is made up of the 
gravitations towards the several particles of which the 
body of the sun is composed, and in receding from the 
sun decreases accurately as the square of the distances 
as far as the path of Saturn . . . . , nay, and even to 
the remotest parts of the paths of comets .... But 
hitherto I have not been able to discover the cause of 
those properties of gravity from phenomena; and I 
frame no hypotheses : * for, whatever is not deduced 
from phenomena is to be called an hypothesis; and 

* The words of Newton, ** Hypotheses non fingo," have been 
often quoted in such sort as to give an entirely incorrect idea of his 
real opinion as to the relation between theoretical and practical 
science. As too commonly understood, they would, in fact, make 
his discovery of gravitation a great exception to his own rule. They 
must be taken in connection with his definition of a hypothesis, as 
** whatsoever is not deduced from phenomena." It is a part of true 
science, nay, it is the highest office of the student of science to 
deduce theories from phenomena. Such research stands as high 
above the simple observation of phenomena as architecture standi 
above brick-making or stone- cutting. But to frame hypotheses as 
the old Greeks did, trusting to the power of the understanding in- 
dependently of the observation of phenomena, is to make bricks 
without straw and to build with them upon the sand. 



46 THE MYSTER Y OF GRA VITY. 

hypotheses, whether metaphysical or physical, whether 
of occult qualities or mechanical, have no place in ex- 
perimental philosophy. ... To us it is enough that 
gravity does really exist, and act according to the laws 
which we have explained, and abundantly serves to 
account for all the motions of the celestial bodies and of 
our sea.'' 

^' Hitherto I have not been able to discover the cause 
of the properties of gravity." Such is the simple state 
ment of the man who discovered those properties. 

And now let us inquire a little into this law of gravity, 
not with the hope of explaining this great mystery of 
nature, — though, for my own part, I believe that the 
time is not far distant when the progress of discovery 
will enable man to make this approach towards the mys- 
tery of mysteries, — but in order to recognise the real 
nature of the mystery, which is a very different thing 
from explaining it. 

In the first place the study of gravity brings us at once 
to the consideration of the infinitely minute, — at least of 
what is for us practically infinite in its minuteness. If 
we consider the above quotation attentively, we perceive 
that this quality of gravity was recognised by Newton. 
" It is not the quantity of the surfaces of particleSy^ he 
says, '' but the quantity of solid matter which they con- 
tain," that gives to gravity its power. Gravity resides in 



THE MYSTERY OF GRAVITY. 47 

the ultimate particles of matter. We cannot conceive of 
matter so divided, no matter how finely, that non-gravi- 
tating particles could be separated from gravitating par- 
ticles. Without entering into the question what atoms 
are, we perceive that these ultimate constituents of 
matter must contain, each according to the quantity of 
matter in it, the gravitating energy. Only, observe how 
incongruously we are compelled to speak. (It is always 
so when we deal with the infinite, Vv^hether the infinitely 
great or the infinitely minute.) We are speaking of 
atoms as the ultimate constituents of matter, and yet we 
are compelled, in describing their gravitating energy, to 
speak of the quantity of matter contained in each atom, 
— in other words, we speak in the same breath of an 
atom as not admitting of being divided or diminished, 
and of its containing matter by q.uantity, that is, by more 
or less. May we not, however, reasonably accept both 
views? The reasoning is sound by which science has 
proved that, so far as our material universe is concerned, 
there is a limit beyond which the division of matter can. 
not be supposed to go, — insom^uch that Sir W. Thomson 
has indicated the actual limits of size of the atoms com- 
posing matter. Yet, passing in imagination beyond the 
bounds of our visible universe, and so entering into the 
next order of universe below it (in scale of construction), 
— the ether of space, — the atoms of our universe may be 



48 THE MYSTERY OF GRAVITY, 

infinitely divisible in that universe, may be, in fact, com- 
pared with its particles, as the suns and worlds of our 
universe are to our atoms and molecules. 

But while gravity thus draws us to the contemplation 
of the infinitely minute, it also leads us to the considera- 
tion of what is for us the infinitely vast. 

Newton was only able to speak confidently of the 
action of gravity at the distance of Saturi), the remotest 
planet knov/n in his day. He did, indeed, refer to the 
comets as probably obeying, even in the remotest parts 
of their paths, the force of the sun's gravity; but he 
could not be certain on that point, because in his time 
no comet had been proved to travel back to the sun 
after receding to the remotest portion of its track. We 
now know not only that the sun's attraction extends to 
the farthest parts of the solar system, having thus a 
domain in space nearly thirty times larger than the 
sphere of Saturn, but we perceive that many among the 
stars exert a similar force ; for around them travel other 
stars even as the planets travel around the sun. Thus 
we know that gravity is exerted in regions lying hundreds 
of thousands of times farther from the sun than Saturn 
is. We have, indeed, every reason to believe, not only 
that star unto star extendeth this mysterious attractive 
influence, but that the least particle in the inmost depths 
of sun or world exerts in full force on each particle, even 



The mystery of gravity. 49 

of suns lying millions of times beyond the range of the 
most powerful telescope yet constructed by man, the full 
energy corresponding (i.) to the (quantity of matter in 
itself and such particle, and (ii.) to the distance separat- 
ing each from each. 

This is amazing enough; but there is something 
more perplexing and mysterious in gravity even than 
this. Not only does gravity lead us to consider the 
infinitely minute in space on the one hand, and the 
infinitely vast in space on the other, but also it leads us 
to consider the infinitely minute and the infinitely vast in 
time also, and this in such a way as to suggest a diffi- 
culty which, as yet, no man has been able to solve. 

Light travels, as we know, with a velocity so enormous, 
that, by comparison with it, all the velocities we are 
familiar with seem absolutely as rest. But gravity acts 
so quickly that even the velocity of light becomes as rest 
by comparison with the velocity of the propagation of 
gravity. Laplace had occasion, now nearly a century 
ago, to inquire whether a certain change in the moon's 
motion, by which she seemed to be gradually hastening 
her motion round the earth, might not be caused by the 
circumstance that gravity requires time for its action to 
te propagated over great distances. He found that if 
the whole of that change had to be explained in this 
way, which would be giving to gravity the slowest admis- 

4 



so THE MYSTERY OE GRAVITY. 

sible rate of transmission, the velocity with which gravity 
is propagated would be eight million times greater than 
the velocity of light. If, on the other hand, that change 
in the moon^s motion could be satisfactorily explained in 
some other way, then the velocity of gravity must be at 
least 16,000,000 times greater than the velocity of light. 
He himself soon after discovered what was in his day 
regarded as a complete explanation of the hastening of 
the moon's motion ; and though in our own time Adams 
of Cambridge has shewn that only half the hastening 
can be accounted for by Laplace's reasoning, the general 
explanation of the remaining half is that it is not a real 
hastening of the moon, but is only an apparent hastening 
caused by the gradual slowing of the earth's rate of 
turning on her axis. This makes the day by which we 
measure the moon's motion seem longer (very slightly, 
however)."*^ Supposing, however, half the moon's hasten- 
ing were left unexplained, and that the non-instantaneous 
transmission of gravity were the only way of accounting 
for it, even then it would be certain that gravity is pro- 
pagated at a rate exceeding 12,000,000 times the velocity 
of light. 

Indeed, at present, owing to the more exact observa^ 

* The point is explained in a paper called * ' Our Chief Timepiece 
Losing Time,** in the first series of my ** Light Science for Leisure 
Hours." 



THE MYSTERY OF GRAVITY, 51 

tions available, and the greater range of time over which 
they extend, it may safely be said that the rate of propa- 
gation of gravity is far greater than this. It is even held 
by some that gravity acts instantaneously over any dis- 
tance, however vast. 

Although I cannot here indicate the exact nature of 
the reasoning by which the enormous rapidity of the 
action of gravity is inferred, I must briefly indicate the 
general argument, that the reader may not suppose the 
matter to be merely speculative. Suppose that the action 
of gravity were propagated at the same rate as light. 

M 

;\ ^ --- 

Fig. 6. 

Then the earth would feel the pull of the sun eight 
minutes or so after she had been in the place where the 
sun began to exert that particular pull. The direction 
of the pull then would not be that of the straight line 
connecting the earth and sun at the moment when the 
pull was felt, but that of the straight line connecting the 
sun and the earth eight minutes or so before. For in- 
stance, when the earth is at Ep fig. 6, the sun at S would 
begin to exert a pull in the line Ei S, but the earth would 
only feel this pull when she got to Eo, her place eight 
minutes later, when it would act upon her in the direc- 



52 THE MVSTER V OF GkA VI T\^. 

tion E^ F, parallel to E^ S. Now this pull, E2 F, may be 
divided into two parts, one along E^ S, pulling the earth 
towards the sun S, the other along E2 T in the earth's 
course, hastening her therefore. But the maintenance 
by the earth of the same constant track depends entirely 
on the action of gravity sunwards. If there is any action 
in addition, hastening the earth, then she w^ill not keep 
her course," but will travel in a constantly widening path? 
—or, in a sort of spiral, very slowly retreating from the 
sun, but retreating constantly. The change of distance 
would not be measurable in millions of years ; but the 
increase in the length of the year would^ before long, be 
observable. Because there is no such increase, astro- 
nomers feel well assured that gravity is not only propa- 
gated more swiftly than light, but many times, even, as 
we have seen, many millions of times, more swiftly. 

It is then in an infinitely minute time that the action 
of gravity traverses all ordinary distances. The earth's 

* In the popular, but incorrect way of speaking, the balance 
between the centrifugal and the centripetal force will no longer be 
maintained : the increase of velocity will give the centrifugal force 
the advantage, and it will slowly draw the body away from the 
centre. In reality there is no centrifugal y2?;r(?, the only force acting 
on the earth in her course round the sun being the sun's attraction 
upon her, which, however, must keep bending her course from the 
straight line, if she is to maintain her distance. In the case above 
imagined it would not bend her course actively enough. 



THE MYSTERY OF GRAVITY. 53 

pull on the moon takes less than the 50,000,000th part 
of a second in reaching the moon, — and the particles 
constituting the mass of the earth act on ourselves, and 
on all the objects which lie near the earth's surface, in 
far less than the io,ooo,oooth part even of this utterly 
minute time-interval. 

Yet age after age has passed during which this 
infinitely active force has been at work without dimi- 
nution, and age after age will continue to pass without 
any change in its activity. For millions of millions 
of aeons it has lasted and will last, so permanent is 
it; while its operation is felt simultaneously at points 
millions of millions of star-distances apart What 
infinities of distance has this wonderful attractive 
force traversed ! 

But even these considerations do not present the 
greatest of the marvels of gravity. It is wonderful, in- 
deed, to consider a form of attraction possessed by the 
infinitely minute, and exerted over the infinitely vast, 
operating in portions of time immeasurably small, and 
extending its operations throughout time infinite. But 
the mystery of mysteries is not here. The marvel of 
marvels is this, that, so far as we can perceive, the force 
of gravity is exerted without any material connection 
with the objects moved by it. Matter seems to act 
where it is not, to use the phraseology of the schools. 



54 



THE MYSTERY OF GRAVITY. 



Of this " action at a distance," Newton himself said, that 
it is inconceivable, that in point of fact it is impossible. 
" No man," he said, " who has, in philosophical matters, 
a competent faculty of thinking," can "for a moment 
believe that a body can act through a vacuum, without 
the intervention of anything else by or through which the 
force may be conveyed from one body to another." Yet 
this is precisely what gravity seems to do. The ether 
occupies, indeed, all space; but there is nothing at 
present known to us by which we can understand how 
the either can transmit the force of gravity. The power 
of the ether in the rapid transmission of undulations 
seems to attain its limit in the propagation of light and 
heat and electricity at the rate of nearly 200,000 miles 
per second. How the ether can act so as to serve as a 
medium of communication between bodies at all dis- 
tances, transmitting impressions 10,000,000 times faster, 
at least, than light travels, nothing at present known to 
us enables us to say. I have, in a lecture which I gave 
in America upon the mysteries of the universe, indicated 
a way in which gravity may be conceived to be generated 
and transmitted ; and I may hereafter describe the con- 
ception (based partly on the views of Le Sage). But it 
is only a conception. There is no phenomenon (except 
the very form of attraction which has to be explained) 
tending to show that the conception is correct And 



THE MYSTERY OF GRAVITY. 55 

even if it be accepted, it brings us face to face with 
only greater marvels. 

At present, however, let this simply be said in con- 
clusion — that the apparent action of gravity at a distance 
is, of all physical wonders, the greatest yet known to 
man. If we accept the opinion of Newton, which, in- 
deed, seems to me indisputable, that matter cannot act 
through a vacuum, then we must admit the existence of 
properties, as yet unthought of, in the ether of space, or 
in some still more subtle universe permeating that ether. 
If, on the other hand, we accept the belief that matter 
can act at a distance, then is there no miracle, either of 
those believed in by mankind generally, or of those more 
generally rejected, which exceeds in marvellousness this 
wonder of all the wonders of physical science. 



V, 



777^ END OF MANY WORLDS. 




SIGN has recently appeared in the heavens 
which has been interpreted in a way sug- 
gesting that many worlds like our own have 
undergone a terrible catastrophe, every living creature 
upon them being consumed as by fire. I propose briefly 
to consider some of the thoughts suggested by this 
strange event. 

It is difficult when we look at the star-lit heavens, 
suggestive as they are of solemn peace, to conceive 
the stupendous energy, the fierce uproar and tumult, 
of which even the faintest visible star in reality tells 
us. Pythagoras spoke of the harmony of the celestial 
spheres, which we are only prevented from hearing by 
its continuity. " There's not the smallest orb which thou 
b^holdest," said the science of the middle ages, 



THE END OF MANY WORLDS. 57 

** Eut in his motion like an angel sings, 
Still quiring to the young-eyed cherubim." 

The science of our own time tells us a still stranger story. 
There's not the smallest orb which thou beholdest, she 
says, but in his motion throbs like a mighty heart, still 
pulsating life to the worlds which circle round it. But 
while our powers of vision are limited to the narrow 
range of our present telescopes, we cannot watch the 
action of these great centres of energy, nor can w^e 
hope that the uproar of those remote fires will ever 
reach mortal ears, though to the mind's ear clear and 
distinct. It is no longer a mere fancy that each star is a 
sun. Science has made this an assured fact, which no 
astronomer thinks of doubting. We know that in certain 
general respects each star resembles our sun. Each is 
glowing like our sun with an intense heat. Around 
each, as around our sun, are the vapours of many 
elements. In each the fires are maintained, as they 
are maintained in our sun, in some way which may be 
partly mechanical, partly chemical, but w^hich certainly 
does not in the least resemble combustion. We know 
that in each star processes resembling in violence those 
taking place in our own sun must be continually in 
progress, and that such processes must be accom- 
panied by a noise and tumult compared with which 
all th^ forms of uproar known upon our earth are a^ 



58 THE END OF MANY WORLDS. 

absolute silence. The crash of the thunderbolt, the 
bellowing of the volcano, the awful groaning of the 
earthquake, the roar of the hurricane, the reverberat- 
ing peals of loudest thunder, any of these, or all 
combined, are as nothing compared with the tumult 
raging over every square mile, every square yard, of 
the surface of each one among the stars. 

If we remember this when we hear of stars varying in 
brightness, we shall perceive that the least change which 
could be recognised from our remote stand-point must 
represent an accession or falling off of energy correspond- 
ing to far more than all the energies existing on our 
earth, or indeed on all the members of the solar system 
taken together. Astronomers recognise our sun as in 
one sense a variable star; for we can hardly suppose 
that he shines with the same degree of brilliancy when 
many spots mark his surface as when he is quite free 
from spots ; and astronomers know that these changes in 
the sun's condition correspond to wonderful changes 
in his activity. When spots are most numerous, the 
coloured flames rage with fierce energy over his whole 
globe, metallic vapours are shot forth from below his 
visible surface with velocities of many miles per second. 
Whereas, when he has no spots, the coloured flames sink 
down from their former height of tens of thousands of 
miles, t*ll they are but a few thousand miles in height \ 



THE END OF MANY WORLDS. 59 

while metallic vapours are seldom emitted, and never 
to the same height, or with the same velocity, as w^hen 
the spots are most numerous. But though the sun thus 
varies in condition, and probably in his total brightness, 
we cannot suppose that such variations could be recog- 
nised from the distance of even the nearest among the 
fixed stars. ' What, then, must be the nature of changes 
taking place in a star, that we, at our enormous dist- 
ance, should be able to recognise them ! We may well 
believe that the entire aspect of such a star must be 
changed to the inhabitants, if such there are, of worlds 
circling around them. 

If, however, the changes taking place in stars, whose 
variations of brightness can just be recognised, must be 
amazing, how stupendous must be the changes affecting 
a star w^hich alternates from brightness to invisibility, 
like Mira, the Star Wonderful, in the constellation of 
the Whale ! how destructive those affecting a star Uke 
Eta, of the ship Argo, which has varied from the fourth 
magnitude to a lustre nearly equalling that of Sirius, and 
thence to the lowest limit of visibility, in the course of 
the last hundred years ! 

Even these changes, however, though justly regarded 
as among the chief w^onders and mysteries of the star- 
depths, seem in turn to sink into nothingness by com- 
parison with the sudden appearance of a new star, as 



6o THE END OE MANY WORLDS, 

interpreted by modern scientific observations. Of old, 
when a new star appeared, it was thought for awhile to 
be a fresh creation ; a new sun set in the centre of a new 
system of worlds, — a thought which was not then so 
startling as in our own times it would be reckoned. 
When the new star was seen slowly to die out until at 
last it became invisible, men were content to regard it as 
a sign set in the heavens for a special purpose. Nor did 
they find much difficulty in associating such a phenome- 
non with some event of importance occurring during 
its continuance, or soon after the new star had died out. 
Such were the explanations offered respecting the ex- 
ceedingly bright star which made its appearance in the 
constellation Cassiopeia in the year 1572. The place 
in which it appeared is shown in fig. 7. It must have 
sprung into its full glory in a very short time, for Tycho 
Brahe, the celebrated astronomer, tells us that, returning 
on November i, 1572, from his laboratory to his dwelling- 
house, he saw the new star, which he was certain had not 
been visible an hour before, shining more brightly than 
any before seen. It surpassed all the stars in the heavens 
in brilliancy, and even Jupiter when that planet is at its 
brightest. Only Venus at her brightest was superior to 
fhe new star. For three weeks it shone with full lustre, 
after which it began slowly to decline. Being situated 
in a part of the heavens always above the horiz;on (for 



THE END OF MAKry WORLDS, 



t\ 



European observatories), the star's entire history could 
be followed. It remained for sixteen months steadfast 
in its position like the other stars. As it decreased in 
size it varied in colour. ''At first," says an old writei; 
*' its light was white and extremely bright ; it then be- 



:^:^ltra^:: 



'CKf-Wf'Wv>m 



^ig. 7. — Cassiopeia ; showing where a new star appeared in the year 1572. 

came yellowish ; afterwards of a ruddy colour like 
Mars j and finished with a pale, livid white, resembling 
the colour of Saturn." 

In passing it may be remarked that there are reasons 
for expecting the return of Tycho Brahe's star in the 



62 • THE END OE MANY WORLDS, 

course of a few years. For other new stars have been 
recorded as seen in the same part of the heavens in the 
5^ears 945 and 1264, and though the interval from 
to 1264 (ox 319 years) exceeds by 11 years the interval 
from 1264 to 1572 (or 308 years), yet the difference is 
but small by comparison with either entire interval; 
and we may not unreasonably believe that the three new 
stars seen in Cassiopeia have been only three apparitions 
of one and the same star, which shines out, with superior 
lustre, for a few months, once in a period averaging 
about 313 years. It seems to me not at all unlikely that, 
some time during the next twenty years, astronomers 
will have an opportunity of examining, with the tele- 
scope and spectroscope, a star which last appeared before 
either instrument had been invented. 

Already facts are known respecting the so-called new 
stars which will not permit us to accept the explanations 
of old so readily offered and admitted, simply because so 
little was certainly known. 

In the year 1866 a star appeared suddenly in the 
constellation of the Northern Crow^n, where no star had 
before been visible to the naked eye. It was a little 
below the arc of stars forming the celestial coronet* 

* Its place is indicated in my School Atlas, as well as (of course) 
in my Library Atlas, from the latter of which the small maps illus- 
rating the present article have been pricked off. The new star is 



THE END OP MAA'Y WORLDS, 63 

It shone as a second magnitude star when first seen, but 
very rapidly diminished in lustre. It increased our 
knowledge in two important respects. 

First, on examining Argelander's charts of the northern 
heavens, the new star was found to have been observed 
and charted as a tenth magnitude star, that is, four 
magnitudes below the lowest limit of naked eye vision. 
It was not, then, a new sun, though it might still truly 
be called a new star, in this sense, that it was a new 
member of the set of stars which adorn our skies as seen 
by ordinary vision. 

In the second place, the star was subject to the 
searching scrutiny of spectroscopic analysis, with results 
of a most interesting character. 

The reader is no doubt aware that when the light of 
a star is analysed into its component colours by the 
instrument called the spectroscope, it is found that all 
the colours of the rainbow are present, as in the case of 
solar light, but (also in the sun's case) not all the tints of 
these colours. Certain dark lines athwart the rainbow- 
tinted streak, called the spectrum of the star, indicate the 

marked T in the Crown (Map VIII.), and must not be confounded 
with the star r, as in Roscoe's Treatise on Spectral Analysis, and 
in some astronomical works. The star r is a well known fifth 
magnitude star, which has shone with no perceptible increase or 
diminution of splendour since Bayer's time certainly, and probably 
for thousands of years before. 



64 The end of Many worlds. 

presence of absorbing vapours in the star's atmosphere. 
This general statement is true of every fixed star, though 
the dark lines of some stars differ in number and position 
from the dark lines of others, showing that other absorb- 
ing vapours are present. In the case of the new star in 
the Crown, the usual stellar spectrum was shewn, — a 
rainbow-tinted streak crossed by a number of dark lines. 
But besides these, there were seen four very bright lines, 
— lines so bright that the rainbow-tinted streak appeared 
as a dark background. The meaning of this is well 
understood by spectroscopists. It signifies that besides 
'"0 . the vapours which, being cooler than the star, absorbed 

a portion of its light, and produced the dark lines, some 
vapours were present in the star's atmosphere which 
were a great deal hotter than the star, and so produced 
bright lines. Now two of the Imes corresponded in 
position with two of the well Jcnown lines of the gas 
hydrogen, showing that this was one of the gases which 
had been raised to an unusual degree of heat. 

It was inferred that there had been some tremendous 
disturbance in that remote star, by which the hydrogen 
and some other vapours present in its atmosphere had 
been intensely heated. But astronomers were unable to 
decide whether the disturbance was of Jhe nature of a 
conflagration, the hydrogen actually burning, or whether 
the heat was occasioned in some other way, as by the 



THE END OF MANY WORLDS. 65 

downfall of some immense mass upon that remote sun. 
For burning hydrogen and glowing hydrogen, though 
either could give the observed bright lines, are very 
different things. In the former case a chemical change 
is taking place, as in the case of burning wood or coal ; 
the latter case resembles that of redhot iron, which is 
not burning itself (not changing into a different form as 
everything does which burns), though it will burn other 
things, — in the ordinary, and incorrect, use of the ex- 
pression. 

The general belief was that there had been a downfall 
of matter on the star in the Crown, by which the whole 
globe of that sun had been excited to an intense degree 
of heat, especially at the surface^ near which lies the 
hydrogen atmosphere of the star. 

I must leave, however, to the next part, the further 
Consideration of the strange thoughts suggested by the 
outburst of this star. I wish to use the small space 
remaining at present to indicate the place where another 
new star burst forth last" November, so that any readers 
of these pages who have telescopes may know where to 
look for a sun which is now dying out, but was shining 
a few weeks ago as a third magnitude star. Fig. 8 
presents a portion of the well-known constellation 
Cygnus or the Swan. Any star atlas will indicate the 
place of the lettered stars shown in the figure. The 



THE END OF MANY W0RL3S^ 



constellation itself does not show at all well at this 
season of the year/'' The part shown in the figure is 
close to the horizon, and directly under the pole-star, at 



1 




Fig. 8.— Part of Cygnus, showing the place of new star (November 24, 1876). 

about half-past ten in the middle of February; but a 
little higher up, between north and north-east, at mid- 

* This chapter was first published in February, 1877, when the 
Star was already invisible to the naked eye, 



The end op many worlds, ej 

night. Professor Schmidt, of the Athens Observatory, 
noticed a new star, in the place shown, on November 
24th last. It must have shone out suddenly, for 
Schmidt had been observing in that region on the night 
of November 22 nd (the last preceding clear night). It 
has since gradually faded, until now a small telescope is 
required to show it, shining as a seventh magnitude star, 
with a well-marked orange tint. 

We have now to consider the history of this star, and 
discuss the general questions suggested by the sudden 
blazing out of suns which had for many years, and 
probably for many centuries, shone continuously with a 
far feebler lustre. It is clear that we have good reason 
to be interested in these questions, seeing that, for 
aught we know, our sun may be one of those exposed 
to sudden great increase of lustre. 

It seems certain, in the first place, that this star leapt 
very suddenly to its full splendour. Schmidt had been 
observing the same regions of the heavens only two 
evenings before, and is sure the star was not then 
shining visibly to the naked eye. Again, astronomy 
is now studied by so many persons, and so many more 
who are not students of astronomy are now well ac- 
quainted with the constellations, that it is very diffi- 
cult for a new star to shine many hours without being 



6S THE END OF MANY WORLDS. 

detected. For example, the new star in the Cro^vn, 
which appeared in May, 1866, though not so well 
placed for observation, was detected by many observers 
at widely distant stations within a few hours of each 
other. It is probable that the star acquired its full 
lustre in a few hours at the utmost, and quite possible 
that, had any one been watching the place where the 
star appeared, he would have heen able to see the star 
grow into full brightness by visible change of lustre, 
just as the lustre of a. revolving light in a distant light- 
house visibly waxes and wanes. It may be, of course, 
that the increase of the star from its ordinary lustre, 
up to the stage when first it was visible to the naked 
eye, occupied many days, or even many months or 
years ; but it seems more likely that as the later stages 
of increase were rapid, so also was the entire develop- 
ment of the new lustre. In that case, if there were 
inhabited worlds circling around that remote sun, they 
had but brief warning of the fate in store for them, as 
presently to be described. 

Like the star in the northern Crown, the new star in 
Cygnus was subjected to the searching scrutiny of the 
spectroscope. The results, though similar in general 
respects, were even more interesting than in the case 
of the brighter new star. In the interval between 1866 
and 1876 spectroscopic analysis has developed largely. 



THE END CF MANY WORLDS. 69 

It has thus become possible to analyse more completely 
the light even of faint stars than the light of bright stars 
could be analysed a decade of years since. 

The spectrum of the new star as examined by ]M. 
Cornu, of the Paris Observatory, showed the bright lines 
of hydrogen, indicating the presence of enormous 
quantities of glo\ving hydrogen, in a state of intense 
heat. But beside these bright lines, others also could 
be seen. One of these was an orange -yellow line. It 
\nll be understood that the faint spectrum of a star 
cannot be so readily lengthened by increasing the dis- 
persion as a bright spectrum; for with too great dis- 
persion the light fades out altogether. And though this 
is not strictly the case with the bright lines, which are 
merely thrown farther apart by dispersion, yet still it 
remains true that one cannot deal with a star spectrum 
e\'en of bright lines as one can with the solar spectrum. 
So that ]M. Cornu was not able to determine whether 
the orange-yellow line belonged to sodium, or to 
that other substance, whatever it may be, which pro- 
duces the orange-yellow line seen in the spectrum of 
a solar prominence."'' Another bright line, green in 

* It will be remembered by those familiar with the history of 
solar observation, that when the spectrum of the solar prominence 
was first observed, the orange-yellow bright line was supposed to 
be the well-known double sodium line. It is so near to this pair 



70 THE END OF MANY WORLDS. 

colour, agreed In position with a triple line belonging 
to the metal magnesium. Lastly, a bright yellowish- 
green line was seen, which is known to be present in 
the spectrum of the sun's corona and of the low-lying 
ruddy matter round the sun, called the sie7'ra by some, 
and by others (apparently unfamiliar with the Greek 
language) the chromosphere. 

Now all this agrees very well with what had been 
noticed in the case of the star in the Northern Crown. 
For, unquestionably, if a sun increases so much in heat 
and lustre that the hydrogen outside it glows more 
brightly than the body of the star, then other matter 
outside that sun might also be expected to share the 
great increase of heat. We see that, outside our own 
sun, hydrogen, a certain unknown vapour of an orange 
yellow colour, magnesium, and another unknown vapour 
of greenish-yellow colour are present in enormous 
quantities ; and it seems, therefore, reasonable to be- 
lieve that other suns have these gases extending far out- 
side the rest of their substance. It is certain that, if 
our sun were caused to glow with far more than its 
present degree of heat, the gases whose increase of 
brightness would be most discernible from a distant 

of lines, that while they are called D i and D 2, it has been called 
D 3 ; and in a spectroscope of small dispersive power the thre^ 
would be seen as one. 



1 



7 HE END OF MANY WORLDS. 71 

Station (as a world circling around some remote star) 
would be just those gases which were glowing so re- 
splendently around the star in Cygnus last November — 
or rather at the time when that light which reached 
us last November set out from the remote star in the 
Swan. 

When we view the outburst of that remote sun 
in this way the thoughts suggested are not altogether 
satisfactory. That sun shows far too much resem- 
blance to our own, and behaved, so far as can be 
judged, far too much as our own sun would behave if 
roused to many times its present degree of heat and 
splendour. When we hear of a railway accident it is 
a matter of special interest to us (if we travel much) 
to learn whether the conditions under which the 
accident took place resembled those under which the 
trains proceed by which we chiefly travel. When an 
express train suffers in such a way as to show some 
special danger arising from great velocity, we find our- 
selves to some degree concerned personally in the in- 
vestigation which follows, if we travel generally by quick 
trains. If a bridge breaks down, and we have often 
to traverse bridges in railway journeying, we are simi- 
larly concerned, especially if any of the 'bridges we have 
to cross resemble in structure the one which has given 
way. So c^ko of rnany other special forms of danger 



72 THE END OF MANY WORLDS. 

in railway travelling. Now, on the same principle, 
we cannot but regard with considerable interest the 
circumstance that, apparently, a catastrophe has taken 
place in the star in Cygnus, which has not only affected 
a sun resembling our own very closely in constitution, 
but has produced effects very closely corresponding to 
those which would affect our own sun if, through any 
cause, he were excited to many times his present degree 
of heat. 

Let us pause a little to reflect upon the effects which 
would follow a great increase of the sun's lustre. A 
change in our own sun, such as affected the star in 
Cygnus, or that other star in the Northern Crown, would 
unquestionably destroy every living creature on the face 
of this earth ; nor could any even escape which may exist 
on the other planets of the solar system. The star in the 
Northern Crown shone out with more than 800 times 
its former lustre : the star in Cygnus with from 500 to 
many thousand times its former lustre, according as we 
take the highest possible estimate of its brightness before 
the catastrophe, or consider that it may have been very 
much fainter. Now, if our sun were to increase tenfold in 
brightness, all the higher forms of animal life and nearly 
all vegetable life would inevitably be destroyed on this 
earth. A few stubborn animalcules might survive, and, 
possibly, a few of the lowest forms of vegetation, but 



THE END OF MANY WORLDS. 73 

naught else. If the sun increased a hundredfold in 
lustre his heat would doubtless sterilise the whole earth. 
The same would happen in other planets. The heat 
falling on the remotest members of the solar system 
would not, indeed, be excessive according to our concep- 
tions. But if we regard Neptune, Uranus, Saturn, and 
Jupiter as the abode of life (which, for my own part, I 
consider altogether improbable), we cannot but suppose 
the orders of living creatures in each of these planets to 
be well fitted to exist under the conditions subsisting 
around them. If this is so — as who can for a moment 
doubt ? — a sudden enormous increase in the sun's heat, 
though not making the supply received by those planets 
much greater than, or even equal to, the supply which 
we receive from the sun, v/ould prove as fatal to living 
creatures there as to living creatures on our earth. 

If, then, the sun increased in splendour as the stars 
have increased which the astronomers call new stars or 
temporary stars, there would be an end of life upon this 
earth j and nothing short of either the spontaneous 
development of life, or of the creation of various forms 
of life, could people our earth afresh. Science knows 
nothing of spontaneous generation, and believers in reve- 
lation reject the doctrine. Science knows nothing of 
the creation of living forms, but believers in revelation 
accept the doctrine. Certain it is that if our sun ever 



74 



undergoes the baptism of fire which has affected some few 
among his brother suns, one or other of these processes 
(if creation can be called a process) must come into 
operation, or else our earth and her companion worlds 
would for ever after remain absolutely devoid of life. 

But if our sun, without suffering so great a change, 
underwent a change of less degree, it might well happen 
that though there would be enormous destruction of life 
upon the earth and other planets, some life (presumably 
the strongest and best) would survive. In that case, 
after a long period of time, the earth would again be well 
peopled, and it might even be that the various races of 
terrestrial creatures would be improved, by the desolation 
which the great solar conflagration had wrought. 

It is somewhat curious, considering how little there is 
in the ordinary progress of events to suggest the idea, 
that most of the ancient systems of cosmogony recognised 
the periodical destruction of living creatures on the earth 
by fire as well as by water. Each form of destruction was 
supposed to be brought about by planetary influences. 
The Ecpyrosis, or destruction by fire, was effected when 
all the planets were in conjunction with Cancer; the 
Cataclysm, or destruction by flood, when all the planets 
were in conjunction with Capricorn. Each form of de- 
struction was supposed also to purify the human race. 
** Towards the termination of each era," v>Tites Lyell, 



THE END OF MANY WORLDS, 75 

speaking of these old ideas, '' the gods could no longer 
bear with the wickedness of men, and a shock of the 
elements or a deluge overwhelmed them; after which 
calamity Astrea again descended on the earth, to renew 
the golden age." The Greeks undoubtedly borrowed all 
such doctrines from the Egyptians, who ^^ believed the 
world to be subject to occasional conflagrations and 
deluges, whereby the gods arrested the career of human 
wickedness, and purified the earth from guilt. After 
each regeneration mankind was in a state of virtue and 
happiness, from which they gradually degenerated again 
into vice and immorality.'* 

Considering that we have every reason to believe the 
records of great floods to relate to events which actually 
occurred, however imperfectly remembered, it seems not 
unreasonable to believe that the tradition of great heats 
had its origin in observed phenomena. As neither or- 
dinary conflagi'ations nor volcanic outbursts would have 
suggested traditions of the kind, it would seem not im- 
possible that at certain times our sun may have acquired 
for a time unusual lustre and heat, causing great and 
widely spread destruction among all forms of animal and 
vegetable life. 

This idea may possibly seem to many, especially at 
a first view, too wild to be entertained for a moment. 
Our sun shines^ so f^ir as appears to ordinary observation, 



76 THE END OF MANY WORLDS. 

with steadfast lustre from year to year, and also from age 
to age. If an occasional hot season suggests for a while 
to some that the sun has grown hotter, or a cool season 
that he has grown cooler, the restoration of cool or 
warmer weather, as the case may be, causes the thought 
to be quickly cast on one side that a change of either 
kind has taken place. Again, if we examine the historical 
records of past ages, we find little to suggest the idea, or 
even the possibility, that the sun in former times shone 
with greater splendour or with less than at present. The 
men of those days were formed like the men of our own 
day, and could not have supported any much greater de- 
gree of heat or of cold than men can support at present. 
Any sudden accession (or diminution) of solar light and 
heat, such as we are considering, would certainly have 
attracted marked attention, and have been recorded for 
the benefit of future ages. The geologic record, again, 
does, indeed, suggest variations in the sun's emission of 
heat as constituting one among the few available ex- 
planations of the existence of tropical forms of life in 
certain strata and of arctic forms in other strata. But 
even if this explanation be the true one, which is by no 
means established, such variations must of necessity have 
been slow, the condition of increased heat continuing for 
many ages in succession, and the like with the condition 
of diminished heat, We have no evidence, historical or 



The end op many worlds, 77 

geological, of the occurrence of any sudden accession 
of solar heat, followed by a quick return to the normal 
temperature, unless we find such evidence in the tradition 
prevalent among Egyptian, Indian, and Chinese cosmo- 
gonists, that at certain recurring epochs in the past our 
earth has undergone destruction and renovation by fire. 

Yet, as I shall now show, it appears that the one only 
natural interpretation w^hich can be given of the outburst 
of a new or temporary sun indicates an event which might 
happen to our own sun, and an event which if it happened 
at all would happen periodically. Moreo^^er, while it will 
appear that there is no reason for fearing the possible 
occurrence (which would, in such case, be really the 
recurrence) of such a catastrophe in the case of our own 
sun as has affected the stars in the Crown and in Cygnus, 
there is no reason for rejecting as incredible the idea that 
catastrophes very serious in their character may have 
affected our sun ; and there is abundant reason for 
believing that small alterations in the sun's total emis- 
sion of light and heat take place very often, in some cases 
periodically ; in others— so far as we can yet judge — 
periodically. 

Lastly, it will be seen that there is always a possibility 
that our own or any other sun may undergo precisely 
such a change as the stars in Cygnus and the Northern 
Crown. Some indeed, even among men of science 



78 TH^ END OF MANY WORLDS, 



(as the Abbe Moigno, for example) believe that it Was 
an event of this sort which St. Peter predicted when 
he wrote, that as the old world, being overflowed with 
water, perished, so '' the heavens and the earth which 
are now, by the same word are kept in store, reserved 
unto fire." According to that view, the day of destruc- 
tion will come " as a thief in the night ; in the which 
the heavens shall pass away with a great noise, and the 
elements shall melt with fervent heat, the earth also, and 
the works that are therein shall be burned up." 

Let us consider how the sudden brightness of a new 
star may be explained. 

I must confess that for my own part I do not attach 
much weight to the suggestion once made by Mn 
Huggins, that an actual conflagration had taken place 
in the case of the new star in the Northern Crown. It 
does not seem to me that any process of mere burning 
could account for the enormous accession of light and 
heat which that sun underwent. 

Consider the case of our own sun. His heat is very 
far beyond that which would be given out by any matter 
known to us undergoing any known process of true com- 
bustion. That is to say, if a mass as large as the sun of 
any known substance were caused to burn, under any 
conditions we can imagine, the momentary emission of 



1 



The end oe man^ worlI^s, J9 

heat by that mass would be very much less than the 
momentary emission of heat by the sun. 

Now it is quite conceivable that by some great 
accession of combustible matter, some supply of fuel 
exceeding many times his entire mass, the sun's entire 
emission of heat might be very largely increased. But 
though such an idea is conceivable, it seems altogether 
far-fetched. The conception is, in fact, inadmissible as 
an explanation of the increase of heat of a temporary 
star, not because of the improbability of the sudden 
accession of so enormous a quantity of matter (though 
that improbability is very great), but because if so enor- 
mous a quantity of matter fell upon the sun, many times 
as much heat would be generated by the mechanical 
effect of the impact as by the combustion of the freshly 
received matter. So that even with the daring assump- 
tion here made, combustion would account for only a 
small portion of the increase of light and heat. 

Huggins' idea was indeed somewhat different. He 
supposed that in consequence of some great internal 
convulsion of the sun in the Northern Crown a large 
volume of hydrogen and other gases was evolved from 
the interior, the hydrogen then by burning giving out 
the light corresponding to the bright lines. At the same 
time, the mass of the sun would be intensely heated by 
the surrounding mass of glowing hydrogen. When the 



8o THE END OF MANY WORLDS, 

liberation of gas from the interior ceased the flame 
would die out, and the sun's surface would gradually 
cool. But if we judge by the case of our own sun, the 
heat of the burning hydrogen would be nothing near 
so great as the heat of the glowing hydrogen already 
outside and within the visible globe of a sun. 

On the whole it seems altogether more probable that 
the accession of splendour observed in the case of tem- 
porary stars is due to the downfall of enormous masses 
of matter upon the surface of these suns. It is, no 
doubt, well known to most of my readers that the down- 
fall of meteoric matter upon the surface of our own sun 
has been considered a sufficient explanation of the sun's 
entire emission of light and heat. The theory that the 
sun's heat and light a7^e thus excited has long since 
been abandoned; but not because the cause would be 
insufficient. It has been abundantly proved that a 
downfall of meteors, not sufficient in quantity to add 
appreciably to the sun's size in many thousands of years, 
would generate more heat and light than he emits in 
that time. The meteoric theory has been abandoned 
simply because it has been shown that no such down- 
fall is taking place. 

The reason why meteoric impact would suffice to 
warm the sun to his present temperature if the meteoric 
showers were heavy, and to warm him far beyond his 



THE END OF MANY WORLDS, 8i 

present temperature if for a few days very heavy meteoric 
showers fell upon him, is simply that his attraction upon 
matter approaching him from without is capable of 
generating a tremendous velocity. We know that when 
a cannon-ball strikes a metal target, with a velocity 
perhaps of some 400 yards per second, great heat is 
excited, and there is a momentary flash of light. If the 
velocity were doubled, the quantity of heat would be 
doubled also. Conceive, then, the tremendous heat 
which would be excited if a cannon-ball could be caused 
to strike a target with a velocity exceeding that just named 
some 1500 times ! The ball and target would both be 
vaporised by the shock, if — which, however, could never 
happen — the target resisted the blow and brought the 
ball to rest. Now matter which reaches the sun from 
without, under the influence of his tremendous attraction, 
strikes his globe with a velocity 1500 times greater than 
that of a cannon ball striking a target at a distance of two 
or three hundred yards. The heat excited is, therefore, 
very intense ; and if meteors were showering at all times 
and in dense flights upon the sun's surface, we should 
require no other explanation of the sun's heat. 

But it appears that meteoric systems are neither so 
numerous nor so rich as to account for the sun's uniform 
emission of heat, though occasional meteoric showers 
upon the sun may be heavy enough to increase appreci- 



82 THE END OF MANY WORLDS, 

ably the amount of heat he emits. It would seem, from 
experiments which have been made by Professor Piazzi 
Smyth, of the Edinburgh Observatory, and later by the 
Astronomer Royal at Greenwich, that from time to time 
the sun's emission of heat really is greater than usual. 
It seems not at all improbable that the increase is due to 
the occasional fall of large masses of meteors in great 
numbers upon the sun. 

Again, it seems that such falls occur periodically, 
or rather that at regular intervals great meteoric 
streams pour upon the sun's surface. For instance, 
the periodic increase and decrease in the number of 
sun-spots is accompanied (so far as we can judge by 
the observations made at Edinburgh and Greenwich) 
by an accession and diminution of the solar heat ; and 
if the change is attributed to the passage of a meteoric 
stream athwart the sun, we should have to assign 
to such a stream a period of rather more than eleven 
years. This, from what we know about the association 
between meteors and comets, would correspond simply 
to the existence of a comet whose path intersects the 
sun's globe, and which is followed by a train of milHons 
of large meteoric masses, many of which are consumed 
at each passage of the rich portion of the train athwart 
the globe of the sun. This comet must of necessity be 
inconspicuous, since it has hitherto escaped detection. 



^ 



THE END OF MANY WORLDS, 83 

In fact, its head and nucleus must long since have been 
entirely destroyed. Only the meteoric train, far more 
widely scattered, remains, simply because at each passage 
past the sun, though many are captured, far greater 
numbers get safely past. 

I am careful to remind the reader that though I 
have, for convenience, used the indicative mood in 
describing these matters, I am in reality presenting 
merely a theory. It may be that the solar spots and 
the accessions of heat are produced in some other way. 
But I must admit I find strong reasons for regarding 
as probable the general theory, that the alternations 
of solar activity (not the solar activity itself be it 
noted) are excited from without. And since we know, 
as a matter of fact, that meteors exist in enormous 
numbers within the solar system, and that they 
aggregate with rapidly increasing density in the sun's 
neighbourhood, we must believe that they fall upon the 
sun in enormous numbers. We also perceive that the 
supply cannot be uniform, but must vary greatly from 
time to time j while what we know about the periodicity 
of meteoric showers on our own earth suggests the belief, 
we may almost say the certainty, that there must be 
periodic downfalls of very heavy meteoric showers upon 
the sun's surface. A\'e have, then, strong probability in 
favour of the belief that events may occur which, ij 



84 THE END OF MANY WORLDS. 

they occurred, might be expected, with a high degree of 
probability, to produce effects resembling those actually 
observed, — viz., the production of a heat more intense than 
usual, accompanied by signs of great disturbance like the 
sun-spots. It does, therefore, seem at least not improb- 
able that these accessions of heat and these signs of great 
disturbance really are brought about in the way supposed. 

A further argument in favour of the meteoric origin of 
solar alternations of heat is to be found in the fact that, 
on one occasion at least, a solar phenomenon, corre- 
sponding precisely to what we should expect to see. if 
great meteoric masses fell upon the sun, has been followed 
by precisely the same signs of terrestrial disturbance 
which accompany and follow the formation of great 
solar spots. I refer to the remarkable occurrence wit- 
nessed by Carrington and Hodgson (at different obser- 
vatories) in September, 1859, when two intensely bright 
points of light were seen travelling beside each other at 
the rate of about 120 miles per second along a short arc 
of the sun's surface, — an arc only equal in length to some 
four-and-a-half times the diameter of our earth. 

On that occasion the emission of solar heat may or 
may not have been increased in an appreciable degree 
for several minutes. My own belief is that it must have 
been ; but we certainly have no means of proving that it 
was. What we do l^now certainly is, that on that day all 



THE END OE MANY WORLDS. 85 

the phenomena which usually accompany the existence 
of many and large sun-spots showed themselves with 
exaggerated intensity. The magnetic needle was greatly 
disturbed, auroras displayed their coloured streamers in 
both hemispheres, telegraphic communication was inter- 
rupted, and everything tended to show that a disturbance 
of the same general character as that which produces 
sun-spots, but much more active while it lasted, had 
affected the sun. It seems, then, altogether reasonable 
to infer that sun-spots are due to the same cause as the 
disturbance which then occurred. So that if we con- 
clude, with most astronomers competent to form an 
opinion, that the disturbance witnessed by Carrington 
and Hodgson was due to the downfall of two very large 
meteoric masses upon the sun, it would follow that sun- 
spots are due to more wide-spread meteoric showers, not 
consisting of masses so large. 

The reader will long since have guessed, no doubt, to 
what all this tends. If the periodical variations of the 
sun's surface are due to meteoric and cometic systems 
whose orbits intersect the sun's globe, their periods being 
short (that is, lasting but a few years), it may well be 
that more important meteoric and cometic systems inter- 
secting the sun's globe exist, which have much longer 
periods. When next one of these makes its passage 
athwart the sun, far more important solar disturbances 



86 THE END OP MANY WORLDS. 

may take place than those which occur when the regularly 
recurring systems salute the sun. Two or three times in 
the history of science comets have approached very 
close to the surface of the sun, as in 1680, and again in 
1843, but without actually impinging upon it. Very 
slight changes in the motions of those comets, owing to 
the disturbing influences of the planets, would cause their 
very nuclei to strike the sun, and their meteoric trains 
to pour afterwards in a full stream upon him for many 
days, or even for many months and years in succession. 

Now I do not think our sun would necessarily suffer 
very much from any of these known comets. They 
may long since have parted with the greater quantity of 
their substance. But it is quite possible that even one 
of those well-known comets of the solar system might 
cause very serious outbursts of solar heat and light ; and 
it is certainly not only possible but extremely probable 
that other comets, such as have visited the solar system 
on paths fortunately not bringing them near to the sun, 
w^ould have worked much mischief had their paths been 
diiferently situated. 

We know that Newton held this opinion. He con- 
sidered the real danger from comets to reside, not 
in the possibility that one might strike our earth, but 
in the possibility that one, falling upon the sun, might 
excite that orb to a degree of heat so intense that 



The end of many Worlds, ^7 

all life on this earth would be destroyed. It is true 
that, in Newton's time, physical laws were not so well 
understood as at present, and a considerable portion 
of Newton's reasoning was consequently inexact. But 
nothing which is now known opposes itself to the belief 
which Newton adopted on this subject. On the contrary, 
whereas Newton only recognised the danger arising from 
the consumption of a comet as fuel for the sun, we now 
recognise a far more serious danger, from the force of 
meteoric impact, and the heat excited as the thermal 
equivalent of the destroyed velocities. Of this part of 
the danger Newton had no clear conception, the relations 
between mechanical energy and heat not having been 
established until quite recent times. 

It appears to me, however, that the danger in the 
case of our own sun — or may we not say our danger ? — 
arises only from the possibility that some one of the 
comets which visit us from the star-depths may make 
straight for the sun; and this danger is exceedingly 
small. Almost certainly a comet which, leaving the 
domain of another sun, falls under the attractive influence 
of our own, would approach him on a path passing 
many millions of miles from his surface. The chances 
against a more direct approach are so great that they 
may be regarded as, to all intents and purposes, over- 
whelming. A comet nii^ht visit us from the star-depth 



M THE END OF MANY WORLDS, 

on a destructive course, just as a single black ball might 
be drawn at the first trial from a bag containing a million 
white balls and only that single black one. But the 
danger is exceedingly small. 

We see, indeed, that other suns have suffered in this 
way, assuming cometic downfall to be the true cause of 
stellar outbursts. There are so many millions of suns^ 
however, in the region of space to which telescopic 
survey extends that the occurrence of ten or twelve such 
outbursts in the course of four or five centuries need not 
be regarded as implying any serious danger. Moreover, 
all the suns which have thus suffered lie within a par- 
ticular region of the heavens,— viz., in the Milky Way, 
and in that half of the Milky Way which is most irregu- 
lar, one may almost say raggedy in structure. (With one 
exception — the star in the Northern Crown, which, never- 
theless, lies on a faint outlying streamer of the Milky 
Way not discernible to ordinary vision.) If then our sun 
belongs to this region of space, the danger for him and 
for us is somewhat greater than my previous argument 
would indicate. For, in that case, we must compare the 
number of outbursts, not with the total number of stars 
within telescopic range, but with the number of those 
stars which lie within this particular region of space. On 
the other hand, if our sun does not lie within that region 
of space, the danger for him and for us is very much 



THE END OF MANY WORLDS. 89 

less ; for instead of a certain small number of accidents 
among his fellow suns, there have been no such accidents, 
only accidents affecting other suns which must be dif- 
ferently classed. 

The case may be compared to the estimation 
of the dangers, let us say, of travelling by ocean 
steamships on a particular route. If we take the 
total number of accidents, for instance, to steamships 
travelling between England and the United States, we 
should estimate the risk of the journey as very small, the 
number of passengers who have lost their lives being 
very small compared with the number who have made the 
journey. But even this small risk is diminished if we 
estimate the danger for a passenger by Cunard steam- 
ships, simply because no passenger has yet lost his life 
through accident to one of these Cunard vessels. 

So in the case of our sun, the danger of an outburst 
such as has affected the stars in the Northern Crown and 
Cygnus is small enough when we estimate it by com- 
paring the number of such accidents with the total 
number of stars, but vanishes almost into nothingness 
when we note that no insulated star like our sun 
seems hitherto to have undergone one of these tre- 
mendous catastrophes. 

But as regards the fate of worlds circling round suns 
which have suffered in this way, we can form but one 



9(5 fHE END OF MANY WORLDS. 

opinion. Beyond all doubt, if such worlds existed and 
were inhabited when their central orb blazed forth with 
many hundred times its former lustre, all life must have 
perished from their surface. We may believe, as many 
do, that no conditions are too unlike those we are 
familiar with on earth to render life impossible ; that the 
creatures subsisting in a world exposed to the most fiery 
heat or to the most intense cold are adapted as perfectly 
to the conditions under which they subsist as we are to 
the circumstances of terrestrial life. But even adopting 
this view, though it seems to accord ill with what we 
know of our own earth, — where life ceases towards the 
polar and over large tracts of the equatorial regions, — we 
could not believe that creatures thus adapted to the 
conditions prevailing around them could endure an 
entire change of those conditions. With the accessions 
of heat in the stars in Cygnus and the Crown, such 
change must inevitably have taken place. Therefore, as 
I think, we must regard the catastrophes affecting those 
remote suns as assuredly involving " The End of many 
Worlds.^' 

iV^/^.— What is stated in the latter portion of this chapter applies 
now only to the star in the Northern Crown ; for the star in Cygnus 
has not faded into a small star, but into a small nebula ! For the 
further,-,history of this star, the reader is referred to my forthcoming 
treatise entitled, '* Pleasant Ways in Science." 



VL 




THE AURORA BORE ALTS. 

^MONG the objects in view, when the recent 
Polar expedition was fitted out, was the hope 
that during the winter of 1875-76 the scien- 
tific observers who accompanied the expedition might be 
able to study the Aurora Borealis under unusually favour- 
able conditions. This hope was, as most of my readers 
doubtless know, disappointed. Few auroras were seen, 
and those seen were not remarkable either for brilliancy 
or for beauty of colour. Yet in the very disappointment 
of the hope which had been entertained on this subject 
there was very significant evidence respecting the aurora, 
as will presently be shown. The quiescence, at that 
time, of the forces which produce the auroral streamers 
had its meaning, and a very strange one. 

The aurora is one of those phenomena of nature which 
are characterized by exceeding beauty, and sometimes by 



92 THE AURORA BOREALIS. 

an imposing grandeur, but are unaccompanied by any 
danger, and indeed, so far as can be determined, by any 
influence whatever upon the conditions which affect our 
well-being. Comparing the aurora with a phenomenon 
akin to it in origin — lightning — we find in this respect 
the most marked contrast. Both phenomena are caused 
by electrical discharges ; both are exceedingly beautiful. 
It is doubtful which is the more imposing so far as visible 
effects are concerned. When the auroral crown is fully 
formed, and the vault of heaven is covered with the 
auroral banners, waving hither and thither silently, now 
fading from view, anon glowing with more intense 
splendour, the mind is not less impressed with a sense 
of the wondrous powers which surround us than when, 
as the forked lightnings leap from the thundercloud, 
the whole heavens glow with violet light, and then 
sink suddenly into darkness. The solemn stillness of 
the auroral display is as impressive in its kind as the 
crashing peal of the thunderbolt. But there is a striking 
contrast between the feelings with which we regard the 
safe splendours of the aurora and the terrible glory of 
the lightning flash. One display we contemplate with the 
calmness engendered by absolute security; the other 
—no matter how little the fear of death may affect the 
reason — cannot be regarded without exciting the con- 
sciousness of danger. We witness in safety, so far as 



THE AURORA BOREALIS. 93 

itself IS concerned, the flash whose light illuminates the 
cloud masses above and around us, but for aught we 
know it may be the last we shall ever see, since no man 
killed by lightning ever saw the flash which brought his 
death. 

I do not purpose to consider here at any length those 
facts respecting the aurora which properly find their place 
in text-books of science, but those only which are less 
commonly dealt with, and seem at once most suggestive 
and most perplexing. 

The reader is no doubt aware that auroras, or polar 
streamers, as they are sometimes called, are appearances 
seen not around the true poles of the earth, but around 
the magnetic poles, which lie very far away from those 
geographical poles which our arctic and antarctic sea- 
men have in vain attempted to reach. We in England, 
though much nearer to the north pole than the inhabi- 
tants of Canada, see far fewer auroras than they do, and 
those we see are far less splendid, simply because we are 
farther away from the northern magnetic pole. This will 
be seen from the accompanying pair of maps (from my 
" Elementary Physical Geography "), showing where the 
northern and southern magnetic poles lie. Again, you 
^^ill see from the northern map, that from England 
the northern magnetic pole lies towards the west of due 
north. That is why when we see a fully developed 



94 



THE AURORA BOREALIS. 



auroral arch in this country its crown Hes towards the 
west of north (almost midway between north and north- 
west). I may have occasion at another time to consider 
the curious changes which affect the actual position of 




i 



Fig. 9-— The Northern Magnetic Meridians and Lines of Equal Dip. 

\!iit magnetic poles and lines ; in this place I merely note 
that what is now said respecting them only refers to the 
present time. 

The formation of auroral streamers around the mag- 
netic poles of the earth shows that these light? ^re due 



THE AURORA BORE ALTS. 95 

to electrical discharges, just as the general magnetic 
phenomena of the earth indicate the existence of electri- 
cal currents. The earth, in fact, with its envelope of air, 
moist and dense near the surface, rare and dry above 




Fig. 10. — The Southern Magnetic Meridians and Lines of Equal Dip. 

may be regarded as an enormous magnetic instrument, 
a core surrounded by conducting matter, in which elec- 
trical currents pass whenever the condition of the earth's 
magnetism changes. The discharges of electricity, 
though only visible at night, take place in reality in the 



96 THE AURORA BOREALIS. 

daytime also. According to their extent and position, 
varying with the varying conditions under which they 
take place, their aspect changes. Moreover, from 
different parts of the earth the appearance of the aurora 
is different. From low latitudes (I speak now of magnetic 
latitudes as indicated by the closed curves around the 
magnetic poles in the maps), the auroral arch is seen 
towards the north in our hemisphere, towards the south 
in the other hemisphere. From points nearer the mag- 
netic pole it is seen overhead, and when that pole is 
approached still nearer, the crown of the arch is seen on 
the side remote from the pole, — that is, towards the 
south in our hemisphere, towards the north in the 
southern hemisphere. 

Remembering that the aurora is due to electrical dis- 
charges in the upper regions of the air, it is interesting to 
learn what are the appearances presented by the aurora 
at places where the auroral arch is high above the hori- 
zon, — these being, in fact, places nearly tinder the auroral 
arch. M. Ch. Martins, who observed a great number 
of auroras at Spitzbergen in 1839, thus writes (as trans- 
lated by Mr. Glaisher) respecting them : " At times they 
are simple diffused gleams or luminous patches ; at 
others, quivering rays of pure white which run across the 
sky, starting from the horizon as if an invisible pencil 
were being drawn ever the celestial vault ; at times it 



THE AURORA BOREALIS. 97 

stops in its course, the incomplete rays do not reach the 
zenith, but the aurora continues at some other point j a 
bouquet of rays darts forth, spreads out into a fan, then 
becomes pale, and dies out. At other times long golden 
draperies float above the head of the spectator, and take 
a thousand folds and undulations as if agitated by the 
wind. They appear to be but at a slight elevation in 
the atmosphere, and it seems strange that the rustling 
of the folds as they double back on each other is not 
audible. Generally, a luminous bow is seen in the north ; 
a black segment separates it from the horizon, the dark 
colour forming a contrast with the pure white or bright 
red of the bow, which darts forth rays, extends, becomes 
divided, and soon presents the appearance of a luminous 
fan, which fills the northern sky, and mounts nearly to the 
zenith, where the rays, uniting, form a crown, which in 
its turn darts forth luminous jets in all directions. The 
sky then looks like a cupola of fire ; the blue, the green, 
the yellow, the red, and the white vibrate in the palpi- 
tating rays of the aurora. But this brilliant spectacle 
lasts only a few minutes ; the crown first ceases to emit 
luminous jets, and then gradually dies out; a diffused 
light fills the sky ; here and there a few luminous patches, 
resembling light clouds, open and close with incredible 
rapidity, like a heart that is beating fast. They soon get 
pale in their turn, everything fades away and becomes 

7 



98 THE AURORA BOREALIS, 

confused, the aurora seems to be in its death-throes ; the 
stars, which its light had obscured, shine with a renewed 
brightness ; and the long polar night, sombre and pro- 
found, again assumes its sway over the icy solitudes of 
earth and ocean." 

The association between auroral phenomena and 
those of terrestial magnetism has long been placed 
beyond a doubt. Wargentin in 1750 first established 
the fact, which had been previously noted, however, by 
Halley and Celsius. But the extension of the relation 
to phenomena occurring outside the earth — very far 
away from the earth — ^belongs to recent times. 

The first point to be noticed, as showing that the 
aurora depends partly on extra-terrestial circumstances, 
is the fact that the frequency of its appearance varies 
greatly from time to time. It is said that the aurora was 
hardly ever seen in England during the seventeenth 
century, though the northern magnetic pole was then 
much nearer to England than it is at present. Halley 
states that before the great aurora of 17 16 none had 
been seen (or at least recorded) in England for more than 
eighty years, and no remarkable aurora since 1574. In 
the records of the Paris Academy of Sciences no aurora is 
mentioned between 1666 and 17 16. At Berlin one was 
recorded in 1707 as a very unusual phenomenon; and the 
one seen at Bologna in 1723 was described as the first 



THE AURORA BOREALIS. 99 

which had ever been seen there. Celsius, who described 
in 1733 no less than three hundred and sixteen observa- 
tions of the aurora in Sweden between 1706 and 1732, 
states that the oldest inhabitants of Upsala considered 
the phenomenon as a great rarity before 1 7 1 6 . Anderson, 
of Hamburg, states that in Iceland the frequent occur- 
rence of auroras between 17 16 and 1732 was regarded 
with great astonishment. In the sixteenth century, how- 
■ ever, they had been frequent. 

Here, then, we seem to find the evidence of some 
cause external to the earth, as producing auroras, or at 
least as tending to make their occurrence more or less 
frequent. The earth has remained to all appearance 
unchanged in general respects during the last three 
centuries, yet in the sixteenth her magnetic poles have 
been frequently surrounded by auroral streamers ; during 
the seventeenth these streamers have been seldom seen ; 
during the last two-thirds of the seventeenth century 
auroras have again been frequent ; and during the present 
century they have occurred sometimes frequently during 
several years in succession, at others very seldom. 

Let us inquire a little more closely into the circum- 
stances attending auroral displays, in order to ascertair 
what external cause it is which thus influences their 
occurrence, 

Connected as auroras are with the phenomena of 



roo THE AURORA BOREALIS. 

terrestrial magnetism, we may expect to find some help 
in our inquiry from the study of these phenomena. 

Now it appears certain that magnetic phenomena are 
partly influenced by changes in the sun's condition. We 
may well believe that they are in the main due to the 
sun's ordinary action, but the peculiarities which affect 
them seem to depend on changes in the sun's action. It 
is found that the daily oscillation of the magnetic needle 
corresponds with the diurnal change in the position of 
the sun owing to the earth's rotation. An annual change 
affecting that oscillation depends on the varying distance 
of the sun as the year proceeds. The daily change is 
not only greater than the annual, but is characterized by 
irregularities, when the face of the sun shows the greatest 
number of spots. It was found by General Sabine, says 
Mr. Balfour Stewart, ^^ that the aggregate value of mag- 
netic disturbances at Toronto attained a maximum in 
1848, nor was he slow to remark that this was also 
Schwabe's period of maximum sun-spots. It was after- 
wards found, by observations made at Kew, that 1859 
(another of Schwabe's years) was also a year of maximum 
magnetic disturbance. . . . There is also some reason to 
believe that on one occasion our luminary was caught 
in the very act. On the first of September, 1869, ^wo 
astronomers, Carrington and Hodgson, were independ- 
ently observing the sun's disc, which exhibited at that 



THE AURORA BOREAUS. lOl 

time a veiy large spot, when, about a quarter past eleven, 
they noticed a very bright star of light suddenly break 
out over the spot and move with great velocity across the 
sun's surface. On Mr. Carrington sending afterwards to 
Kew Observatory, at which place the position of the 
magnet is recorded continuously by photography, it was 
found that a magnetic disturbance had broken out at the 
very moment when this singular appearance had been 
observed." The dip of the. magnetic needle^ its- deflec- 
tion from the north, the inferiority of its directive force, 
were all three simultaneously and abruptly altered, and 
continued so for many hours. 

Nor are we left in any doubt as to the connection 
between such well-marked disturbances of the magnetic 
nee-dle. While the needle was thus violently displaced, 
vivid auroras occurred over the greater part of both the 
northern and southern (magnetic) hemispheres. They 
were seen in latitudes where usually auroras are as in- 
frequent as rain in Peru, — at Rome, in the West Indies, 
even within eighteen degrees of the equator. 

The disturbance of the earth's electrical condition was 
well shown in other ways. Mr. C. V. Walker, the tele- 
graphist, found that strong electrical currents affected the 
various telegraphic lines throughout England. These 
currents changed in direction every two or three minutes. 
In many places it was impossible to send telegraphic 



102 THE AUItORA BOREALtS, 

messages. In America some of the signalmen received 
severe electric shocks. '^ At a station in Norway," says 
Sir J. Herschel, '^ the telegraphic apparatus was set fire 
to ; and at Boston, in North America, a flame of fire 
followed the pen of Bain's electric telegraph (which writes 
down the message upon chemically prepared paper)." 

Many of my readers will doubtless remember the 
auroras of May 13, 1869, and October 24, 1870, both 
of which occurred when the sun's surface was marked 
by many spots, and both of which were accompanied by 
remarkable disturbance of the earth's magnetism. 

It may, then, fairly be assumed that the occurrence of 
auroras depends in some way, directly or indirectly, on 
the condition of the sun. But what the real nature of 
that connection may be is not to be easily determined. 
It Is clear that the eleven-year-period of sun-spots is not 
the only, or even the chief period affecting auroras, for 
we have seen that sometimes for a full century, or even 
more, very few auroras are seen. It is not by any means 
certain that the connection between the sun's condition 
and the occurrence of auroras is of the nature of 
cause and effect ; quite probably sun-spots and auroras 
depend on some common cause as yet undetected, — and 
possibly never to be detected by man. 

Regarding the auroral streamers as terrestrial lights 
only, but in some sense like the light reflected by planets 



THE AURORA B0REAL13. IO3 

in having their real source in the sun, we can no longer 
speak, as Humboldt was wont to do, of our planet 
possessing a power of emitting light of its own. Yet 
his manner of dealing with auroral light still possesses 
interest for us, especially in relation to the question 
whether these polar lights are emitted by other 
planets and may possibly be discerned from our earth. 
"It results from the phenomena of the aurora," said 
Humboldt, " that the earth is endowed with the pro- 
perty of emitting a light distinct from that of the sun. 
The intensity of this light is rather greater than that 
of the moon in its first quarter. It is at times, as on 
January 7, 1831, strong enough to admit of one's read- 
ing printed characters without difficulty. This light 
of the earth, the emission of which towards the poles 
is almost continuous " (this, however, is not strictly the 
case), " reminds us of the light of Venus, the part of 
which not lighted by the sun often glimmers with a dim 
phosphorescent light. Other planets may also possess 
a light evolved out of their own substance." 

I would venture, however, to express strong doubts 
as to the possibility of discerning, either on Venus or 
on any other planet, the auroral gleams which may 
very probably illuminate at times their nocturnal skies. 
It must be remembered that the aurora, when at its 
brightest and covering a large part of the sky, orly 



104 THE AURORA BOREALIS, 

gives about as much light as the moon in her first 
quarter, — that is, as one half of a disc so small that 
180,000 such discs would not equal the entire sky. 
The luminosity of the aurora is then in reality very 
small ; probably far less than that of the earth's sur- 
face when illuminated by the full moon. A distant 
hill on which the rays of the full moon are falling 
seems strongly illuminated, and yet its light is teally 
so faint that we could scarcely discern it at all save 
for the favouring effect of contrast. We know this, 
because we often see portions of the moon's surface 
which are illuminated by earthshine (when we see what 
is called the old moon in the new moon's arms), and 
these portions are quite faint by comparison with the 
rest of the moon; yet earthshine exceeds moonshine 
at least twelve times, and probably more nearly twenty 
times in splendour. 

The glimmering phosphorescent light, supposed to 
have been seen on parts of Venus not lighted by the 
moon, is a phenomenon about which experienced tele- 
scopists are somewhat doubtful, though Webb speaks 
of the appearance as remarkably well attested, quoting, 
amongst others, the following cases. In 17 15, Derham, 
in his " Astro-Theology," says that " the sphericity or 
rotundity is manifest in our moon, yea, and in Venus, 
too, in whose greatest falcations " (t.e,, when they appear 



THE AURORA BOREALIS. 105 

as crescents) '^the dark parts of their globes may be 
perceived, exhibiting themselves under the appearance 
of a dull and rusty colour." In 1806, the phenomenon 
displayed itself beautifully to Harding three times 
and to Schroter once within five weeks. *' Guthrie and 
others noticed it a few years ago, with small reflectors, 
in Scotland; Purchas, at Ross, in England; De Vico 
and Palomba, many times in Italy." Winnecke re- 
cords a similar observation, though very faint, 187 1, Sep- 
tember 25, a little before noon. Van Hahn also says 
he saw it repeatedly, by day as well as by night, and 
\\ith several instruments ; he was, however, an inferior 
observer. The dark side is sometimes described as grey, 
sometimes as reddish; The phenomenon has, on the 
other hand, been looked for specially, on several occa- 
sions, by practised observers, using very fine instru- 
ments, who have failed to recognise any trace of it. 

One of the most remarkable observations ever made 
on Venus must here be mentioned. Madler states that 
on one occasion, when he was observing the planet, 
he saw a number of brushes of light diverging from the 
circular side (/>., the outside of the planet's crescent), 
lasting as long as the planet could be seen that even- 
ing, and remaining unchanged when he changed the 
position of the telescopic eye-piece, or used a different 
one. " He attempts no explanation/' says Webb, ** but 



I06 THE AURORA BOREALtS. 



% 



thinks it could not have been an optical illusion. This 
is certainly possible^ but it is an instructive instance of 
the oversights which may be incidental even to great 
philosophers, that it never seems to have occurred to 
him to try another telescope ! " It cannot be doubted 
that the evidence would have been greatly strengthened 
had he changed telescope as well as eye-piece ; though 
it is not readily to be explained how a known telescope, 
frequently used as well before as after this strange 
appearance was seen, could for one evening only have 
played so strange a trick as Madler's must have done, 
if what he saw was merely an instrumental illusion. 

However, whether we have telescopic evidence or not 
respecting auroral lights surrounding the polar regions 
of other planets, we can have very little doubt that 
some among the planets, if not all of them, resemble 
our earth in this as in so many other respects. The 
aurora is a cosmical phenomenon, not one peculiar 
to cur own earth. It is not, indeed, altogether certain 
that our sun himself may not be girt round by mighty 
auroral streamers, and that the light of these may not 
constitute a noteworthy portion of the corona of glory 
seen around him during the time of total eclipse. 

This view, indeed, although it has not been definitely 
entertained as I have here expressed it, has been sug- 
gested by reasoning which led others to suppose that the 



THE AURORA BOREAU^. lo? 

coloured prominences around the sun may be auroras. 
Perceiving the nature of the connection between terres- 
trial magnetism and auroras, Balfour Stewart reasoned 
that we may extend our inquiries and ask, " If the sun's 
action is able to create a terrestrial aurora, why may 
he not also create an aurora in his own atmosphere ? " 
It occurred independently to General Sabine, Prof. 
Challis, and himself, that the red flames visible during 
a total solar eclipse ^^may be solar aurorae.^' We now 
know that the solar flames are not aurorae, nor, properly 
speaking, flames at all, but great masses of glowing 
vapour. It is not, however, by any means so clear 
that the solar corona is not auroral in its nature. The 
following reasoning, applied by Balfour Stewart to the 
sun's prominences, applies with much greater force to 
the corona. After mentioning the height (from 70,000 
to 80,000) which some prominences attain, he proceeds, 
*' Considering the gravity of the sun, we are naturally 
unwilling to suppose that there can be any considerable 
amount of atmosphere at such a distance from his 
surface; and we are therefore induced to seek for an 
explanation of these red flames amongst those pheno- 
mena which require the smallest possible amount of 
atmosphere for their manifestation. Now the experi- 
ments of Mr. Gassiot and the observed height of the 
terrestrial aurora alike convince us that this meteor 



lo8 THE AURORA BORE A LIS. 

will answer our requirements best. And besides this, 
the curved appearance of these red flames, and their 
high actinic power, in virtue of which one of them, 
not visible to the eye, was photographed by Mr. De la 
Rue, are bonds of union between these and terrestrial 
aurorae." 

All this and much more may be said of the solar 
corona. Its streamers extend not 70,000 or 80,000 
miles, but 700,000 or 800,000 miles , from the sur- 
face of the sun, where the pressure liiust be far smaller 
than near the summits of even the loftiest prominences. 
They are curved and striated, like those of the aurora, 
whereas the shapes of the prominences bear only a 
distant resemblance to auroral streamers. They possess 
a high actinic (/>., photographic) power, as is shewn 
by the readiness with which, during the total eclipse 
of December, 187 1, they were photographed, no less 
than six well-defined negatives being taken both 
by Col. Tennant, at Ootacamund, and by Mr. Davis, 
at Baikal, during the brief continuance (only a few 
minutes) of total obscuration. In every respect the 
solar corona accords far better than do the solar 
coloured prominences with the appearance we should 
expect to recognise in solar auroras. 

In particular, it has always seemed to me that the 
curved, especially the doubly curved, streamers of the 



THE AURORA BO RE A LIS, 109 

corona can only be well explained by regarding the 
corona as in the main an auroral phenomenon. If 
mighty currents prevailed in the higher regions of a 
rare atmosphere, extending hundreds of thousands of 
miles from the sun's surface, appearances such as these 
curved streamers would undoubtedly be explained. But 
no one who considers the effect of the sun's tremen- 
dous attractive power on such an atmosphere can fail to 
perceive that, according to the known laws connecting 
gaseous pressure and density, the density of that atmos- 
phere would be enormously great, even at a very great 
distance from the sun's surface, if the curved streamers 
really were caused by atmospheric currents. We know, 
on the contrary, from the behaviour of comets which 
have passed very near to the sun, that the atmosphere 
above his visible surface must be very rare indeed. 

It must not be understood, however, that I regard 
the corona as simply a great solar aurora. It is certain 
that the whole region filled by the corona is occupied 
by immense numbers of scattered meteors, and extremely 
probable that large quantities of cometic matter exist 
within the same region. Vaporous masses may also be 
there, circling independently around the sun. But that 
this region is illuminated constantly by auroral light, 
varying greatly in intensity and position, seems very 
strongly indicated by all that we know about the 



no THE AURORA BOREALIS, 

corona, as seen during different total eclipses of the 
sun. 

If we so viewed the solar corona, and found our earth, 
therefore, in this respect resembling the great central 
orb of the solar system, we could not but regard as ex- 
tremely probable the theory that other planets also 
resemble the central body in this respect. We might 
then picture to ourselves every orb in the solar system 
carrying onward its faintly luminous crowns of boreal 
and austral light, not shining with constant lustre, or 
in the same constant position, but at one time leaping 
in coloured steamers to a great distance from the body 
they adorned, and anon sinking down and growing 
fainter and fainter, or occasionally disappearing alto- 
gether. Then, when some great disturbance affected 
the central sun, and caused his auroral banners to shine 
out more brilliantly and to attain a greater extension, sud- 
denly the auroral streamers of all the planets would leap 
out into new light and life, playing around the northern 
and southern magnetic poles of those orbs, even as 
electric brushes play around the positive and negative 
electrodes of a Geissler's tube. " Suddenly " at least 
so far as each planet is concerned, but not suddenly 
throughout the whole system. For the magnetic in- 
fluences, like the light and heat of the sun, require 
time for their transmission. Yet, so rapidly do they 



THE AURORA BO RE A LIS, iii 

travel that, in a few hours, the auroral illumination 
would extend from the central sun to the outermost 
Hmits of his system. 

It remains that I should make a few remarks on the 
evidence which that wonderful instrument of research, 
the spectroscope, has afforded respecting the light of 
the aurora. 

Angstrom was the first to observe the spectrum of the 
aurora borealis. He found that the greater part of the 
auroral light, as observed in 1867, was of one colour, 
yellow, but three faint bands of green and greenish 
blue colour were also seen. The aurora of April 15, 
1869, was seen under very favourable conditions in 
America. Prof. Winlock, observing it at New York, 
found its spectrum to consist of five bright lines, of 
which the brightest was the yellow line just mentioned. 
One of the others seems to agree very nearly, if not 
exactly, in position with a green line, which is the most 
conspicuous feature of the spectrum of the solar corona. 
During the aurora of October 6, 1869, Flogel noticed 
the strong yellow line and a faint green band. Schmidt, 
on April 5, 1870, made a similar observation. He saw 
the strong yellow line, and from it there extended to- 
wards the violet end of the spectrum a faint greenish 
band, which, however, at times showed three defined 
lines, fainter, than the yellow line. 



II* THE AURORA BORE A LIS. 

It was not till the magnificent aurora of October 24, 
25, 1870, that any red lines were seen in the spectrum 
of an aurora. On that occasion the background of 
auroral light was ruddy, and on the ruddy background 
there were seen three deep red streamers very well 
defined. The ruddy streamers, on the night of October 
25, converged towards the auroral crown, which was on 
that occasion singularly well seen. Forster of Berlin 
failed to see any red line or band despite the marked 
ruddiness of the auroral light. But Capron at Guild- 
ford saw a faint line in the red part of the spectrum ; 
and Elger at Bedford observed a red band in the light 
of the red streamers, the band disappearing, however, 
when the spectroscope was directed on the white rays 
of the aurora. 

As yet the auroral spectrum has not been interpreted. 
It is not a spectrum which can be (at present) artificially 
produced. We understand the spectrum of the sun and 
stars, because spectra of the same order can be pro- 
duced in our laboratories. The spectra of the planets, 
so far as they differ from the spectrum of reflected sun- 
light in showing signs of the absorptive action of the 
planetary atmosphere, have been similarly interpreted. 
So also the spectra of the coloured solar prominences 
are understood, while those of nebulae and comets, 
though not as yet thoroughly explained, have been 



THE AURORA BOREALIS. 113 

partly interpreted, because of their partial agreement 
with the known spectra of earthly elements. But as 
yet neither the spectrum of the aurora nor that of the 
solar corona has been explained. The reason probably 
IS, that the conditions under which the light of the 
aurora as of the corona is formed are not such as have 
been or perhaps can be attained or even approached in 
laboratory experiments. 



VII. 



THE LUNAR HALO. 

^^^kT^m HERE are some phenomena of nature which 
^^^^^' suggest false ideas. For instance, when we 




look at the broad expanse of ocean on a 
moonlit night, and see a path of glory on its surface, 
directed towards the moon's place, we seem to be assured 
by the sense of sight that that broad track is illuminated 
while the waters all around are dark. A little considera- 
tion, however, assures us that the impression is a false 
one, that in this case seeing is not believing. The moon's 
rays really illumine the whole surface which lies before 
us, and we fail to receive light from other parts than the 
track below the moon, liot because they receive no light, 
but because the light which they receive is not reflected 
towards us. An observer^ stationed a mile or two towards 
the right or towards the left of our station, sees a different 
track of light, while the part which seems bright to us 
seems dark to him. 



THE LUNAR HALO, ii5 

The rainbow is another phenomenon of this decep- 
tive kind. We seem to see an arch of many colours sus- 
pended in the air, — and when we learn that it is due to 
the presence of drops of water in the air, we are apt to 
infer that where we see the red arch there are drops lit 
up with red light, where the yellow, green, or violet arch, 
that the drops are aglow with yellow, green, or violet 
light. But in reality this is not so ; the same drops 
which seem green to us will seem red to another ob- 
server, violet to another, and to yet other observers will 
show none of the prismatic colours, but only the dull 
grey colour of the cloud on which the rainbow is seen. 
We have here a pretty emblem of the varied aspects 
which events of the same real nature present to different 
persons, or according to the dilTerent circumstances under 
which the same person may see them. One shall see 
events in rosy tints, or with the freshness of spring 
hues, or with the melancholy symbolled by the 

• deeper indigo (as when 

The heavy- skirted evening droops with frost)— 

while to others the same events shall show only the 
ordinary tints of common-place Hfe. 

The lunar halo is one of the phenomena thus decep- 
tive to the view. We see all around the moon a circle 
or arc of light, nearly white, though sometimes faint 



lid THE LVNAk itALO. 



% 



tints of colour can be perceived in it, while the space 
within the circle seems manifestly darker than the space 
outside. The appearance of the halo as seen under 
favourable conditions is shown in fig. it, on the next 
page. In this country the dark space round the moon 
is not generally so well seen as in countries where the 
air is clearer. But this is in reality the characteristic 
feature of the halo, as its name shows. For the name is 
derived from a Greek word signifying threshing-floor (the 
old threshing-floors being round), and thus naturally 
describes a round space relatively clear, surrounded on 
all sides by a ring of aggregated matter. 

We seem in looking at the lunar halo, then, to see the 
moon at the centre of a dark space, surrounded by a 
ring of bright particles, outside which again are particles 
not quite so brightly illuminated as those forming the 
ring, but more brightly than those within the ring. 

But in reality this impression, which, so far as the sense 
of sight is concerned, seems forced upon the mind, is 
entirely erroneous. There is no real distinction between 
the space which looks dark all round the moon, the 
space beyond which does not look dark, and the ring 
between the two spaces which looks bright. These are 
all equally illuminated by the moon, in the same sense, 
at least, that we say the surface of a moonlit sea is all 
equally illuminated, neglecting slight differences which 



THE LUNAR HALO. uy 

do not concern the point we are specially dealing with. 
Precisely as the path of light on the ocean is not a 
real path of illumination, bounded on either side by 




-Lunar Halo 

dark spaces, so the ring of light round the moon is not 
a real ring of light, bounded on one side by a less bright 
region, and within by a dark space. 
Although my object in these essays is not specially to 



Il8 THE LUNAR HALO, 

deal with scientific matters, but rather with the thoughts 
(much more important in my beUef) which they suggest 
—so that, in deaUng with my present subject, I wish 
rather to call attention to the manifold ways in which our 
senses may deceive us unless their evidence is carefully 
cross-examined — yet it may be worth while to notice how 
the particular illusion here considered has deceived even 
the scientific elect 

It had been noticed by Tyndall, in certain experi- 
ments, that a very sensitive measurer of heat, when placed 
under the moon's rays, gathered together by a powerful 
condenser, seemed to indicate cooling rather than heat- 
ing, as we should expect. On this a French student of 
science pointed to the darkening under the moon where 
the lunar halo is seen as evidence that our satellite 
possesses a certain power of clearing away vaporous 
matter from the air. " On pent dire, ^^ he said, speaking 
of the dark space within the halo, " que la tune ouvre 
alors tme porie par laquelle s'echappe le calorique que 
r action solai7'e a em7nagasine dans les couches infirieicres,^^ 
" One may say,'' that is, '' that the moon then opens a door 
through which the heat escapes, which the sun's action 
has stored up in the lower layers " (of the air). It will be 
manifest, if we remember that a lunar halo can often be 
seen at the same time from stations hundreds of miles 
apart^ that there can be no such opening of clear air, 



THE LUNAR HALO. 119 

For the cloud layer in which the halo is formea is but 
a few miles above the observer; and therefore, if one 
observer saw a circular opening in this layer, with the 
moon at its centre, another, a hundred miles from him, 
would see the space in a very different direction. The 
moon would not only not be at the centre of the space 
for this second observer, but would not be visible through 
the space at all. Moreover, the space could not possibly 
seem round to both observers ; if it seemed round to 
one, it would look like a very flat oval of darkness 
(almost a mere line) to the other. 

The real explanation of the lunar halo is very different. 
When you see such a halo, you may be certain that there 
is, high up in the air, a layer of light feathery cloud — the 
cirrus cloud, as it is called — composed of tiny crystals of 
ice. These crystals, as we know from those which in 
winter sometimes fall (not as snow, but as little ice-stars),, 
have all a definite shape. They are in fact little prisms 
of ice, with angles like those of an equilateral triangle. 
These little prisms deflect the light which falls upon 
them, just as one of the drops of a chandelier deflects 
any light which falls upon it. If you hold a prism-drop 
of a chandeher between the eye and a light, you will see 
that the prism looks dark ; it is really lit up, but it sends 
the light away in such a direction that the eye receives 
none. Now move it gradually away from the line of 



120 THE LUNAR HALO. 

sight to the Hght, and at a certain distance it appears full 
of light ; or, to speak more correctly, it sends the light 
it receives directly towards your eye. Beyond that posi- 
tion it again looks dark, but not so dark as when it was 
nearly between the eye and the light. 

The little crystals of ice perform the same part with 
respect to the moon, when we see a lunar halo. Those 
between us and the moon, or within a certain distance 
from the line of sight to the moon, are, in reality, lit up 
by the moon's rays ; but they send off those rays in such 
directions that we do not receive the light. Thus, all the 
space lying towards the moon, and for a certain distance 
all round, looks dark. But, at a certain distance, these 
little crystals send us light. If we could see them 
separately, they would seem to be full of light. That is 
the distance where ice-crystals of their known shape act 
most favourably in deflecting light, — that is, send off 
most for all the varying positions (not places) they can 
be in. At greater distances, a small proportion send us 
light. Thus, at that distance we have a ring of light, 
and outside the ring we have a gradual falling off in the 
quantity of light. 

But the reader will be apt, perhaps, to say, How can 
all this be proved ? No one has ever been among the 
ice-crystals of the feathery clouds when they are per- 
forming this work. When Coxwell and Glaisher made 



THE LUNAR HALO. 121 

their highest ascent, the feather-clouds seemed almost as 
high above them as ever. Nor, if any one could reach 
those clouds, could he see the ice-crystals at their work. 
Yet there are few points about which science is more 
certainly assured than about this explanation of the halo. 
For we know the shape constantly assumed by ice-crystals; 
we know according to what precise law ice bends rays of 
light falling upon it ; hence we can calculate quite cer- 
tainly where, if ice-crystals make the halo, its rings should 
be seen. And the halo has the precise position thus cal- 
culated from the known laws of optics, and the known 
facts about ice and ice-crystals. The diameter of the 
halo should be, and is, about eighty times the apparent 
diameter of the moon, or somewhat less than half the 
arc which separates the point overhead from the 
horizon. 

There is, however, yet stronger evidence. Haloes 
form around the sua as well as round the moon,— in fact, 
more frequently. Solar haloes have so much more light 
in them that we can recognise varieties of tint. Now, it 
•follows from the laws of optics that, for the red part of 
the sun's light, the halo ring should have a smaller 
diameter than the halo ring for the violet part, inter- 
mediate colours having their corresponding intermedi- 
ate halo rings. Thus, the halo ring, as a whole, should * 
be rainbow-tinted, red on the inside, then orange, yellow. 



122 THE LUNAR HALO, 

green, blue, indigo, and violet ; and these colours are 
shown (under favourable conditions) in this order. 

The student looking out for haloes, solar or lunar, 
must be careful not to confound them with solar and 
lunar coronas, that is, not the corona of astronomy, but 
rings of light around the sun and moon, much smaller 
than the true halo rings. What I have said above 
about the size of the true halo will suffice to prevent 
such a mistake. Coronas are not nearly so easily, 
though they have been quite as thoroughly, explained 
by science, as haloes. 

It is singular to observe how utterly unlike the in- 
terpretation of the halo by science is from the natural 
interpretation. The observer would say. There surely is 
a dark space all round the moon, and round that a ring 
of light, — I see these things, and seeing is believing. 
Science says there is no dark space, and there is no ring 
of light; while the eye of science perceives something 
where the lunar halo shines which ordinary vision cannot 
recognise. Up yonder, many miles above the earth, 
science sees millions of crystals of ice, carried hither 
and thither — so light are they — by every movement of 
the air. Science sees these ice crystals deflecting the 
rays of moonlight, sifting the red rays from the orange, 
and these from the yellow, yellow from green, green from 
blue, blue from indigo^ and indigo from violet, Science. 



THE LVXAR HALO, 123 

in fine, perceives processes taking place in those higher 
regions of air compared with which the most delicate 
analyses of the laboratory are utterly coarse and im- 
perfect. 

There is a purer and nobler poetry in the lunar halo 
as thus understood than in its mere visible phenomena, 
attractive and beautiful though these are. Idle indeed 
is the fear that the interpretation of this special mystery 
of nature will leave the number of nature's mysteries 
diminished by one. On the contrary, for the one mys- 
tery explained many deeper mysteries are suggested. 
The phenomena discernible by the sense of sight are 
explained, but only by bringing into the range of a purer 
and more piercing vision phenomena infinitely more 
wonderful. If one could see through some amazing 
extension of \isual power, or if even the imagination 
could adequately picture, the rush of light waves of all 
orders of length upon the line of crystal breakers, their 
deflection in all directions, their separation into their 
various orders of wave-length ; if one could perceive the 
actual illumination of the ice-crystals, even where they 
seem dark to us, and the continual fluctuations of the 
troubled sea of ether between the crystal breakers and 
the earth below, — the scene would infinitely transcend in 
interest and mystery, the picture would be infinitely more 
suggestive of solemn thoughts, than the scene — beautiful 



124 THE LUNAR HALO, 

though it doubtless is— presented by the halo-girt moon 
to ordinary vision. Truly they know little of the real 
meaning of science who regard it as depriving natural 
phenomena of their effect on the imagination, as robbing 
Nature of her poetic influence. 



VIII. 



MOONLIGHT. 




iHE light of the moon and the changes of 
the moon were probably the first phenomena 
which led men to study the motions of the 
heavenly bodies. In our times, when most men live 
where artificial illumination is used at night, we can 
scarcely appreciate the full value of moonlight to men 
who cannot obtain artificial light. Especially must 
moonlight have been valuable to the class of men 
among whom, according to all traditions, the first 
astronomers appeared. The tiller of the soil might 
fare tolerably well without nocturnal light, though even 
he, — as indeed the familiar designation of the harvest- 
moon shows us, — finds special value, sometimes, in 
moonlight. But to the shepherd moonlight and its 
changes must have been of extreme importance as he 
watched his herds and flocks by night We can under- 



126 Moonlight. 

stand how carefully he would note the change from the 
new moon to the time when throughout the whole night, 
or at least of the darkest hours, the full moon illuminated 
the hills and valleys over v/hich his watch extended, and 
thence to the tim_e when the sickle of the fast waning 
moon shone but for a short time before the rising of the 
sun. To him, naturally, the lunar month, and its sub- 
division, the week, would be the chief measure of time. 
He would observe-— or rather he could not help observ- 
ing — the passage of the moon around the zodiacal band, 
some twenty moon-breadths wide, which is the lunar road- 
way among the stars. These would be the first purely 
astronomical observations made by man; so that we 
learn without surprise that before the present division of 
the zodiac was adopted the old Chaldean astronomers 
(as well as the Indian, Persian, Egyptian, and Chinese 
astronomers, who still follow the practice) divided the 
zodiac into 28 lunar mansions, each mansion corre- 
sponding nearly to one day's motion of the moon among 
the stars. 

It is easy to understand how the first rough obser- 
vations of moonlight and its changes taught men the 
true nature of the moon, as an opaque globe circling 
round the earth, and borrowing her light from the sun. 
They perceived, first, that the moon was only full when 
she was opposite the sun, shining at her highest in the 



MOONLIGHT. iij 

soiith at midnight when the sun was at his lowest 
beneath the northern horizon. Before the time of full 
moon, they saw that more or less of the moon^s disc was 
illuminated as he was nearer or farther from the position 
opposite the sun, the illuminated side being towards the 
west — that is, towards the sun; while after full moon 
the same law was perceived in the amount of light, 
the illuminated side being still towards the sun, that is, 
towards the east. They could not fail to observe the 
horned moon sometimes in the daytime, with her horns 
turned directly from the sun, and showing as plainly, by 
her aspect, whence her light was derived, as does any 
terrestrial ball lit up either by a lamp or by the sun. 

The explanation they gave was the explanation still 
given by astronomers. Let us briefly consider it. In 
doing so I propose to modify the ordinary text-book 
illustration which has always seemed to me ingeniously 
calculated (with its double set of diversely illuminated 
moons around the earth) to make a simple subject 
obscure. 

In figi 12, let E represent the earth one half in dark* 
ness, the other half illuminated by the rays of the sun S, 
which should be supposed placed at a much greater 
distance to the left, — in fact, about five yards away 
from E. To preserve the right proportions, also, the sun 
ought to be much smaller and the earth a mere point. 



125 



MOONLIGHT. 



I mention this to prevent the reader from adopting 
erroneous ideas as to the size of these bodies. In 

reality it is quite im- 
possible to show in 
such figures the true 
proportions of the 
heavenly bodies and 
of their distances. 
Next let Ml, Mg, Mg, 
etc., represent the 
moon in different posi- 
tions along her circuit 
around the earth at E. 
Now, it is clear 
that when the moon 
is at Mj, her illumi- 
nated face is turned 
from the earth, E. 
She therefore cannot 
be seen ; and accord- 
ingly, in fig. 2, she is 
presented as a black 
disc at I to corres- 
pond with her invisibility when she is as at Mj. She 
passes on to M^ ; and now from E a part of her illumi- 
nated half can be seen towards the sun, which would be 




Cm 



MOONLIGHT, 



129 



towards the right, if we imagine an eye at E looking 
towards Mg. Her appearance then is as shown at 2, 
fig. 13. In any intermediate portion 
between M^ and Mg, the sickle of light is 
visible but narrower. We see also that all 
this time the moon's place on the sky 
cannot be far from the sun's place, for the 
line from E to Mg is not greatly inclined 
to the line from E to S. When the moon 
has got round to M3, the observer on the 
earth sees as much of the dark half as of 
the bright half of the moon, the bright 
half being seen, of course, towards the 
sun. Thus the moon appears as at 3, fig. 
13. Again as to position, the moon is now 
a quarter of a circuit of the heavens from 
the sun, for the line from E to M3 is 
square to the line from E to S. We see 
similarly that when at M^ the moon ap- 
pears as shown at 4, fig 13, for now the 
observer at E sees as small a part of the 
moon's dark side as he had seen of her 
bright side when she was at Mg. When 
she is at M5 the observer at E sees her bright face only, 
the dark face being turned directly from him. She, 
therefore, appears as at 5, fig. 13. Also being now exactly 

9 



c 

5' 

a 



130 MOONLIGHT. 

opposite the sun, as we see from fig. 12, she is at her 
highest when the sun is at his lowest, or at midnight ; 
and at this time she rules the night as the sun rules the 
day.''' As the moon- passes on to M^., a portion of her 
dark half comes into view, the bright side being now 
towards the left, as we look at Mg from E, fig. 12. Her 
appearance, theiefore, is as shown at 5. When at M^ she 
is seen as at 7, half bright and half-dark, as when she was 
at M3, but the halves interchanged. At Mg she appears 
as at 8, and, lastly, at M^ she is again undiscernible. 

The ancient Chaldean astronomers could have litde 
doubt as to the validity of this explanation. In fact, 

"^ It has been thought by some that, in the beginning, the moon 
was always opposite the sun, thus always ruhng the night. IMilton 
thus understood the account given in the first book of Genesis. 
For he says, — 

Less bright the morn, 
But opposite in levell'd west was set 
His mirror, with full face, borrowing her light 
From him"; for other light she needed none 
In that aspect ; and still that distance keeps 
Till night, then in the east her turn she shines, 
Revolv'd on Heav'n's great axle. 

It was only as a consequence of Adam's transgression that he con- 
ceives the angels sought to punish the human race by altering the 
movements of the celestial bodies — 

To the blank moon 
Her office they prescribe — 

It is hardly necessary to say, perhaps, that this interpretation is not 
bcientifically admi sible. 



MOONLIGHT. 131 

while it is the explanation obviously suggested by ob- 
served facts, one cannot see how any other could have 
occurred to them. 

But if they had had any doubts for a while, the occur- 
rence of eclipses would soon have removed those doubts. 
They must early haye noticed that at times the full 
moon became first partly obscured, then either wholly 
disappeared or changed in colour to a deep coppery red, 
and after a while reappeared. Sometimes the darkening 
was less complete, so that at the time of greatest dark- 
ness a portion of the moon seemed eaten out, though 
not by a well defined or black shadow. These pheno- 
mena, they would find, occurred only at the time @f full 
moon. And if they were closely observant, they would 
find that these eclipses of the moon only occurred when 
the full moon was on or near the great circle round the 
stellar heavens, which they had learned to be the sun's 
track. They could hardly fail to infer that these darken- 
ings of the moon were caused by the earth's shadow, near 
which the moon must always pass when she is full, and 
through which she must sometimes pass more or less 
fully; in fact, whenever, at the time of full, she is on 01 
near the plane in which the earth travels round the sun. 
Solar eclipses would probably be observed later. For 
though a total eclipse of the sun is a much more striking 
phenomenon than a total eclipse of the moon, yet the 



132 MOONLIGHT. 

latter are far more common. A partial eclipse of the 
sun may readily pass unnoticed, unless the sun's rays are 
so mitigated by haze or mist that it is possible to look at 
his disc without pain. Whenever solar eclipses came to 
be noted, and we know from the Chaldean discovery of 
the great eclipse period, called the Saros, that they were 
observed at least two thousand years before the Christian 
era, the fact that the moon is an opaque body circling 
round the earth, and much nearer to the earth than 
the sun is, must be regarded as demonstrated. Not only 
would eclipses of the sun be observed to occur only when 
the moon was passing between the earth and the sun, 
but in an eclipse of the sun, whether total or partial, the 
round black body cutting off the sun^s light wholly or 
partially would be seen to have the familiar dimensions 
of the lunar orb. 

Leaving solar and lunar eclipses for description 
on another occasion, I will now proceed to consider 
a peculiarity of moonlight which must very early have 
attracted attention, — I mean the phenomenon called the 
harvest-moon. 

The moon circuits the heavens in a path but slightly 
inclined to that of the sun, called the ecliptic, and for 
our present purpose we may speak of the moon as 
travelling in the ecHptic. Now we know that during the 
winter half of the year the sun is south of the equator, 



MOONLIGHT. 133 

the circle of the heavenly sphere which passes through 
the east and west points of the horizon, and has its plane 
square to the polar axis of the heavens. During the 
other or summer half of the year he is north of the 
equator. In the former case the sun is above the 
horizon less than half the twenty-four hours, day being 
so much shorter as the sun is farther south of the 
equator; whereas in the latter case the sun is above 
the horizon more than twelve hours, day being so much 
the longer as the sun Is farther north of the equator. 
Precisely similar changes affect the moon, only, instead 
of taking place in a year (the time in which the sun 
circuits the stellar heavens), they occur in what is called 
a sidereal month, the time in which the moon completes 
her circuit of the stellar heavens. For about a fortnight 
the moon is above the horizon longer than she is below 
the horizon, while during the next fortnight she is below 
the horizon longer than she is above the horizon. Now 
clearly when the length of what we may call the moon's 
diurnal path (meaning her path above the horizon) is 
lengthening most, the time of her rising on successive 
nights must change least. She comes to the south later 
and later each successive night by about 50^ minutes, 
because she is always travelling towards the east at such 
a rate as to complete one circuit in about four weeks ; 
and losing thus one day in 28, she losses about 50^ 



t34 MOONUGllT. 

miuutes per day. If the inter\-al between her rising and 
her arri\ ing to the south were always the same, she 
would rise 50^ minutes later night after night But if 
the interval is lengthening, say by 10 minutes per niglit, 
she would of course rise only 40! minutes later ; if tlie 
inter\al is lengthening 20 minutes i)er night, she would 
rise only 30 J minutes later, and so forth. But the lunar 
diurnal arc /i^ lengthening all the time she is passing from 
her position farthest south of the equator to her position 
farthest north, just in the same way as the solar day 
is lengthening from midwinter to midsummer, only to 
a much greater degree. And as the solar day lengthens 
fastest at spring when the sun crosses the equator from 
south to north, so the time the moon is above tlie 
horizon lengthens most, day by day, when the moon is 
crossing the equator from south to north. It lengtliens, 
then^ from an hour to an hour and 20 minutes in one 
day, that is, the inten^l between moon-rise and moon- 
setting increases from 30 to 40 minutes. At this time, 
then, whencN'er it happens in each lunar month, the 
moon^s time of rising changes least: instead of the 
moon rising night after night 50J minutes later, the 
actual difference \^es only from 10 to 20 minutes. 

Now if this happens at a time when the moon is 
not nearly full, it is not specially noticed, because the 
moon^s light is not then specially useful But if it 



MOONLK.irr. 135 

happens when the moon is nearly full, it is noticed, 
l)ccaii.se her light is tlieri so useful. A moon nearly full, 
afterwards quite full, and tlien for a day or two si ill 
nearly full, rising nigliL after night at nein-ly the same 
time, remaining also night after night longer ahovc tiie 
hori/on, manifestly ser\'es man for the time being in the 
most convenient way ])ossible. Hut it is clear that as 
the full moon is oi)|)OS!lc the sun, and as to fulfil the 
condition described we have se(.'n that she must be 
crossing the ecjuator from sr)uth to nr)rth, the sun, 
opjxjsite to her, must be at the i)arl of his j>ath where: he 
crosses the equator fiom north U) sr)Utli. In other 
words, the time of year must be the autunmal equinox. 
Thus the moon which comes to '' full " nearest to Sep- 
tember 22 or 23 will behave in the c onsenient way 
described. At this time, moreover, when she rises night 
after night nearly at the same time, the nights are 
lengthening fastest while the time the moon is abo\'e the 
hori/on is lengthening still more, and therefore, in all 
respects, the moon is then doing her best, so to si)eak, 
to illuminate the nights. At this season the mo(;n is 
called the harvest-moon, from the assistance she some- 
times renders to harvesters. 

The moon which is full nearest to Sei>tember 22—23 
may precede or follow thait date. In the former case 
only can it properly be called a harvest-moon. In the 



136 Moonlight. 

latter it is sometimes called the hunter's moon. The full 
moon occurring nearest to harvest time will always par- 
take more or less of the qualities of a full moon occur- 
ring at the autumnal equinox: and similarly of a full 
moon following the autumnal equinox. So that, in almost 
every year, there may be said to be a harvest-moon and 
a hunter's moon. But, of course, it will very often 
happen that in any particular agricultural district the 
harvest has to be gathered in during the wrong half of 
the lunar month, that is, during the last and first, instead 
of the second and third quarters. 

The reader must not fall into the mistake of supposing, 
as I have seen sometimes stated in text-books of astro- 
nomy, that we are more favoured in this respect than the 
inhabitants of the southern hemisphere. It is quite true 
that the same full moon shines on us as on our friends in 
New Zealand, Australia, and Cape Colony, and also that 
our autumn is their spring, and their spring our autumn. 
But the full moon we have in autumn behaves in the 
southern hemisphere not as with us, but as our spring 
full moon behaves; and the full moon of our spring, 
which is their autumn, behaves with them as our autumn 
moon behaves with us. It is, therefore, for them a 
harvest-moon if it occur before the equinox, and a 
hunter's moon if it occur after the equinox. A very 
little consideration will show why this is. In fact if, in 



MOONLIGHT. 137 

the explanation given above, the words north and south 
be interchanged, and March 21 — 22 written for Septem- 
ber 22 — 23, the explanation will be precisely that which 
I should have given respecting the harvest (or March) 
moon of the southern hemisphere, if I had been writing 
for southern readers. 

Having thus considered the moon as a light-giver, 
both in respect of her monthly changes and of that 
yearly change which causes her services to be most use- 
ful in harvest time, let us consider what science tells us 
of the orb which thus usefully reflects to us the solar 
rays. 

The moon is a globe about 2159I miles in diameter, 
travelling round the earth at a mean distance of 238,818 
miles. Her path round the earth is not, however, a 
circle, but an ellipse, which itself is constantly varying 
in shape. The average eccentricity of the moon's path 
is such that her greatest and least distances, as she 
circuits round it, are 251,953 miles and 225,683 miles 
respectively ; but when it is most eccentric, her greatest 
and least distances are 252,948 miles and 221,593 miles 
respectively; while, when it is least eccentric, they are 
respectively 250,324 miles and 227,312 miles. The 
earth's surface exceeds the moon's nearly 13I times, 
the actual number of square miles in the moon's sur- 



138 MOONLIGHT, 

face amounting to 14,600,000. This is nearly equal to 
Europe and Africa together, or, more nearly still, to 
North and South America together, without their 
islands. In volume our earth exceeds the moon rather 
more than 49 J times: or, more nearly, if the earth's 
volume be represented by 10,000, the moon's will be 
represented by 209. The materials of the moon's globe 
are either lighter or (more probably) they are less 
closely compacted than those forming our earth,— 
for, according to the best modern estimates, the earth 
exceeds the moon in mass nearly Z\\ times. Assun>| 
ing as the most probable value of the earth's mean 
density about 5^% times the density of water, the moon's| 
mean density is equal to 3jVo times that of waterJ 
Gravity at her surface is accordingly much less than at' 
the surface of the earth ; a quantity of matter weighing 
six pounds at the surface of the earth would weigh 
almost exactly one pound at the surface of the moon. 

The moon circuits once round the earth in 2 yd. yh. 
43m. 11.5s. This is the time in which, viewed from 
the earth, she seems to complete one circuit round the 
stellar heavens, and is therefore called a sidereal month. 
But as the earth is all the time travelling the same way 
round the sun, the lunar month is longer. Thus, 
suppose S (fig. 14) to be the sun, E the earth at thj 
beginning of a lunar month, M^ M^ M3 M^ the moon's 



MOONLIGHT, 139 

path, and M^ the moon's place on the line joining E 
and S. If the earth remained at rest while the moon 
went round the path M^ M3, then after completing one 
circuit the moon would again be at M^ on the line 
joining E and S, or it would be new moon again. But 
the earth is moving onwards along the arc EE' of her 
circuit round the sun. So that wlicn the moon has 




Fig. 14. — Explaining the difierence between a sidereal lunar month 
and a common lunar month or lunation. 



completed one circuit she is at M4 (E^m^ drawn parallel 
to EMj) and has still to travel some distance before she 
gets round to M' on the line joining S and E'. The 
lunation, or interval between successive new moons, has 
an average duration of 29d. i2h. 44m. 38s., exceeding 
a sidereal month by 2d. sh. 

It would not, however, be correct to regard the earth 



140 MOONLIGHT, 

as the true centre of the moon's motion. The moon is 
in reality a planet circling round the sun, but largely 
perturbed by the attraction of its companion planet 
the earth. If the moon's path in the course of a year 
were carefully drawn to scale, or, better, were modelled 
by means of a fine wire, it would scarcely be distinguish- 
able from a similar picture or model of the earth's path 
round the sun. Or thus, the entire width of the moon's 
track is about 477,636 miles, while the diameter of the 
orbit along which she and the earth both travel is nearly 
104,000,000 miles, or 385 times as great. If we draw 
then a circle Zt^^ inches in diameter to represent the 
earth's path round the sun, somewhat eccentrically placed, 
and the circular line is i-iooth of an Inch wide, the 
moon's track would be fairly represented by a curve 
touching alternately the inside and the outside edge of 
this circular line, at equidistant points dividing the 
circle into about 24I parts. 

Regarding the moon as a planet, she may be said to 
have a year, and seasons, and day and night, as the 
earth has, but very unlike our seasons and days. Her 
axis is inclined only i^ degrees from uprightness to 
her path, whereas our earth's axis is inclined 23^ 
degrees. The sun's range of mid-day altitude is in fact 
not quite equal to the range of our sun in mid-day 
height, from four days before to four days after either 



MOONLIGHT, 141 

spring or autumn. The lunar day lasts a lunar month, 
daytime and nighc-time each lasting rather more than 
a fortnight. The lunar year of seasons is not, as is 
commonly stated, the same in length as ours. She 
goes round the sun in the same time, so that her side- 
real year is the same as ours ; but owing to the sway- 
ing round of her axis her year of seasons or tropical 
year is shorter. Our tropical year is also shorter than 
the sidereal year, but very little shorter, because the 
earth's axis sways round once only in 25,868 years. The 
moon's axis sways round once in i8f years, and accord- 
ingly the year of seasons is much more effectively 
shortened. It lasts, in fact, only 346d. i4h. 34m. of 
our time; and contains only ii| lunar days. So that 
I cannot altogether agree with Sir W. Herschel's state- 
ment, that ^^the moon's situation with respect to the 
sun is much like that of our earth, and by a rotation on 
its axis it enjoys an agreeable variety of seasons, and of 
day and night." 

When the moon is examined with a telescope her 
surface is seen to be marked by many irregularities. 
There are large dark regions which were formerly 
thought to be seas, but are now know to be land- 
surfaces. Some of these regions are singularly level, 
and have been thought to be old sea- bottoms. Moun- 
tains and mountain ranges are anothej important feature 



142 MOONLIGHT. 

of the moon's surface. Some, like our Rocky Mountains 
and Andes, form long continuous chains ; others form 
elevated plateaus whence ridges extend in various direc- 
tions. A very striking form is that of narrow ridges little 
raised above the general level, but reaching over enormous 
areas of the moon's globe. It is a system of this kind, 
radiating from a great lunai crater called Tycho, which 
gives to small photographs of the moon the appearance of 
a peeled orange. They are supposed to indicate the 
action of tremendous forces of upheaval, in past ages, 
bursting open portions of the moon's crust. 

But the most characteristic of all the lunar features 
are the crater mountains, which exist on a scale not 
only much larger relatively to the moon's globe than 
the scale on which terrestrial craters are formed, but 
much larger absolutely. They are also far more nume- 
rous. Some parts of the moon's surface, especially in 
the bright south-western quarter of her face, are literally 
crowded with craters of various dimensions. 

There are few signs of the former emission of lava 
from the lunar craters. Within some of them recent 
changes have been suspected. A remarkable instance 
is that of the crater Linne, marked in Madler's map as 
a deep, well-walled crater, some four miles in diameter. 
At present only a small crater can be seen in its place. 
The surrounding region is rather conspicuously bright. 



MOONLIGHT. 143 

It is not necessary to infer that there has been any 
volcanic disturbance, however. Far more probably the 
walls have been thrown dovv'n through the long-continued 
action of that alternate expansion and contraction, which 
must affect the moon's crust as the long fortnightly day 
proceeds, and then the equally long lunar night. 

There are many well-marked valleys on the moon, 
besides clefts and ravines. The features called rilles are 
among the most perplexing objects on the moon's surface. 
Webb, in his charming and most useful little book, 
"Celestial Objects for Common Telescopes," thus de- 
scribes them : '^ These most singular furrows pass chiefly 
through levels, intersect craters (proving a more recent 
date), reappear beyond obstructing mountains, as though 
carried through by a tunnel, and commence and termi- 
nate with little reference to any conspicuous feature 
of the neighbourhood. The idea of artificial formation 
is negatived by their magnitude ; they have been 
more probably referred to cracks in a shrinking surface." 
Some observations would seem to show that they have 
been formed from rows of closely-adjacent small craters. 
Faults, 2i\^o, or closed cracks where the surface is higher 
on one side than on the other, have been recognised 
from the careful study of the shadows on the moon's 
disc. 

From measurements of the shadows of lunar moun- 



144 MOONLIGHT, 



tains, it appears that their average height is about five 
miles. In comparing this elevation with that assigned 
to terrestrial mountains, it must be remembered that 
these are measured from the sea-level ; if the average 
height of terrestrial mountains were determined with 
reference to the sea-bottom it would be far greater. Still, 
even taking this circumstance into account, the average 
height of the lunar mountains bears a far greater ratio to 
the diameter of the globe on which they stand than the 
average height of our mountains to the earth's diameter. 

Several circumstances agree in showing that the moon's 
atmosphere must be exceedingly rare. The shadows of 
lunar mountains are either actually black or nearly so. 
When the moon hides the sun in total eclipse, no sign 
can be seen of any refractive effort exerted on the sun's 
rays. When a star is hidden (or occulted) by the moon, 
the star vanishes in an instant and reappears with equal 
suddenness. It is certain from these phenomena that 
the moon has either no air, or air exceedingly tenuous. It 
is equally clear that she has no Avater, for if she had we 
should undoubtedly be able to recognise the occasional 
formation or dissipation of mist and vapour over parts of 
the moon's surface. No signs of such phenomena have 
ever been observed. The moon is certainly at present a 
waterless globe, so far at least as her surface is concerned. 

It has been thought that though there is no water and 



% 



hiO ON LIGHT, 145 

very little air on the side of the moon turned towards the 
earth, there may be both water and air on the farther 
unseen side. The theory has been long since given up, 
but the reasoning on which it depends is worth noting. 
Owing to the strange circumstance that the moon rotates 
on her axis in the same time in which she revolves round 
the earth, she always presents the same face towards the 
earth, or very nearly so. If her axis were exactly square 
to the path in which she circuits the earth, and if she 
revolved at a uniform rate, we should have exactly the 
same side constantly turned towards us. But as the axis 
is incHned about 6|" from uprightness to the path round 
the earth (which, be it remembered, is not in the same 
plane as the path round the sun, but inclined 5° 8' 
to it), the northern and southern parts of the moon 
are alternately swayed over by about 6|° into view. 
This apparent swaying is called a libration, and the 
libration just described is called the libration in latitude. 
Again, as the moon does not travel at a uniform rate 
round the earth, but faster than her mean rate when 
nearer to us, and slower when farther from us, she alter- 
nately gains and loses in her motion of revolution as 
compared with her motion of rotation, by a quantity 
varying between 5° and 7f°, to which varying extent the 
parts east and west of her mean disc are alternately 
swayed into view. This is called the libration in 

10 



146 



Moonlight, 



longitude. Thus we see, beyond the edge of the 7nean 
half turned towards us, a considerable fringe of the other 
half. If a globe, as PAP'B, fig. 15, were divided into two 




^\r, 15.— lUus lafng lunar librat'on. 



4 



halves to represent the farther and nearer halves of the 
moon, and held so that that dividing circle were seen as 
PEP' in the figure, then Ppep'P' would represent the 
part brought into view at different times by the apparent 



MOONLIGHT. 147 

swaying described above ; while Vpep'Y* would represent 
the parts swayed out of view. The regions thus alter- 
nately in view and out of view have their greatest breadth, 
not at the poles or east and west, but at mMm and 
m'M'm', where the two librations act together. The 
narrow fringe bordering these regions is that brought 
into or out of view by changes in the place of the observer 
on earth, due to the earth's rotation. It is called the 
parallactic fringe, any change in the apparent position of 
a heavenly body, or part of one, on account of the earth's 
rotation, being termed parallax. 

Lastly, let us return to the consideration of moonlight, 
as depending on the condition of the moon's surface. 
To one who observes the moon as seen on the sky, her 
light appears white ; but it must not be supposed that 
she is a white body. Careful estimates of the quantity 
of light she reflects show that she is more nearly black 
than white, though in reality she is neither one nor the 
other. It has been said, and truly, that if the surface of 
the moon were covered with black velvet she would still 
appear white ; for even black velvet reflects some light, 
and whatever Ught the moon reflected would show her 
by contrast with the blackness of the sky, as a luminous 
body or white. It follows from the observations made 
by Zollner that if the moon's surface were covered with 
white snow she could give us about 4^ times as much 



14^ MOONLIGHT. 

light as she actually does. If she were covered with 
white paper she would give more than 4 times as much 
light as she does. If she had a surface of white sand 
stone her light would be nearly half as great again as it 
is. She gives rather more light than she would if her sur^ 
face consisted entirely of weathered grey sandstone, .or 
of clay marl, and more than twice as much light as she 
would give if her surface were of moist earth, or dark 
grey syenite. As some parts of her surface are obviously 
much brighter than others, we must infer that some 
parts shine with much more, and others with much less, 
brightness than weathered grey sandstone. Probably 
some parts are much brighter than white sandstone, and 
some much darker than dark grey syenite. From the 
degree in which her lustre changes with her changing 
aspect, Zollner infers that her mountains have an average 
slope of about fifty- two degrees. 



IX 




THE PLANET MARS. 

^Y^i^VERY one who notices the stars at all, — 
and who that thinks and can see does not ? 
— must have observed during the autumn 
of 1877 two bright stars in the southern heavens. One 
of these shone with a lustre which but for its ruddy hue 
would have caused the star to be taken for the planet 
Jupiter; the other shone with a somewhat yellowish 
light, and was much fainter, though surpassing most of 
the fixed stars in brightness. The former was the planet 
Mars, the latter the ringed planet Saturn. The motions 
of these two stars with respect to each other and to 
the neighbouring stars were sufficiently conspicuous to 
attract attention. During October these stars attracted 
still more attention, because they drew nearer and nearer 
together, to all appearance, until on November 4th 
they were at their nearest, when the distance separat- 



ISO THE PLANET MARS. d| 

ing them was about one-third the apparent diameter 
of the moon, so that in a telescope showing at one view 
the whole disc of the moon, Mars and Saturn on the 
night of November 4th appeared like a splendid double 
star, the primary a fine red orb, the* companion a smaller 
body, but attended by a splendid ring system and com- 
panion moons. 

It was strange when we looked at these two stars, the 
yellow one apparently much smaller than the brighter, 
and the pair see^^ingly close together, to consider how 
thoroughly the reality differed from these appearances. 
The fainter and seemingly the smaller of the two stars 
was in reality some four thousand times larger than the 
brighter, and had, among eight orbs attending upon it, 
one nearly as large as the ruddy planet which as actu- 
ally seen so completely outshone Saturn himself. Again, 
instead of being near each other, those two bodies were in 
reahty separated by a distance exceeding some sixteen 
times that which separated us from the nearer of the two. 

I propose now to consider some of the more interest- 
ing characteristics of these two planets, presenting specially 
those features which mark Saturn as the representative 
of one family of bodies, and Mars as the representative 
of another and an entirely different family. 

It will be well to consider Mars first ; for although, 
as will presently be seen, Saturn came earlier of the two 



X 



THE PLAXET MARS, 153 

to the portion of his path where he was most favourably 
seen, there was nothing specially remarkable about the 
approach of Saturn on that occasion, whereas Mars in 
the year 1877 made a nearer approach to the earth 
than he has for thirty-two years past, or will for some 
forty-seven years to come. 

In the first place, let us note the apparent paths 
on which the two planets have been and are now 
travelling. 

Fig. 16 presents that part of the zodiac along which lay 
the apparent paths of Mars and Saturn in 1877. The 
stars marked with Greek letters belong to the constellation 
Aquarius, or the Water-Bearer (his jar is formed by the 
stars in the upper right-hand corner of the picture), — with 
a single exception, the star marked k, which, with those 
close to it not lettered, belongs to the constellation Pisces, 
or the Fishes. Thus the loops traversed by the two 
planets in 1877 both fell in the constellation of the 
Water-Bearer ; but, as will be seen from the symbols on 
the ecliptic, these loops lie in the zodiacal sign Pisces, 
which begins at k and ends at T. The signs have long 
since passed away, in fact, from the constellations to 
which they originally belonged. 

It will be noticed that Mars described a wide loop 
ranging to a considerable distance from the ecliptic (or 
sun"s track). Saturn, on the other hand, travelled on a 



154 THE PLANET MARS. 

narrow and shorter loop lying much nearer to the ecliptic, 
his whole track, except just where he was turning, — his 
stationary points, — lying nearly parallel to the ecliptic. 
It may be well to mention the reason of this well-marked 
difference. Mars does not in reality range even quite so 
widely from the plane of the ecliptic as Saturn does. Nay, 
his path is even less inclined to the ecliptic. (This may 
sound like repetition, but the inclination of a planet's 
path to the ecliptic is one thing, the range of the planet 
north and south of the ecliptic, in miles, is another. 
Mercury, for example, has of all planets the path most 
inclined to the ecliptic, but Mercury never attains any- 
thing like the same distance from the plane of the ecliptic 
which is attained by the remote planet Uranus, whose 
path is of all others the least inclined to the plane of 
the ecliptic. In fact, none of the planets, except Venus 
and Mars, have so small a range from the ecliptic in 
actual distance as Mercury has.) The reason why the 
range of Mars from the ecliptic appeared so much greater 
than that of Saturn, in 1877, is similar to the reason why 
Mars, though much smaller than Saturn, largely outshone 
him. Mars looked larger because he was nearer, his loop 
looked larger because his real path was nearer. For the 
same reason that a hut close by seems to stand higher above 
the horizon than a palace at a distance, or a mountain 
yet further away, so the displacement of Mars from the 



THE PLANET MARS, 155 

ecliptic plane appeared greater than that of Saturn, though 
in reality much less. 

Let us consider how the paths of these planets are 
really situated. I know of no better way of showing this 
than by drawing the paths of the two families of planets 
separately. It is in fact utterly impossible to give an 
accurate yet clear view of the solar system in a single 
picture ; and the student may take it for granted that 
every drawing or plate in which this has ever been 
attempted is from one cause or another misleading. 

In figs. 17 and 18 the shape and position of the plane- 
tary paths are correctly shown. Very little description is 
necessary, but it may be mentioned that on each orbit 
the point nearest to the sun is indicated by the initial 
letter of the planet, while the point farthest from the sun is 
indicated by the same letter accented. The places where 
each path crosses the plane of the earth's — which is sup- 
posed to be the plane of the paper — are marked 9> and 
^, the former sign marking where the planet in travelling 
round in the direction shown by the arrows crosses the 
plane of the earth's path from below upwards, while the 
latter marks the place where the planet in travelling round 
crosses the plane of the earth's path from above down- 
wards. 

Fig. 1 7 shows the paths of the inner family of planets 
of which our earth is a member. Fig. 18 showsi:he outer 



156 



THE PLANET MARS, 



family of planets, and inside of it the ring of small 
planets called asteroids. Inside that ring, again, we see 
the paths of the inner family of planets ; but they 




Fig- T7. — The paths of ^Mercury, Venus, the Earth, and Mars, around the Sun. 



appear on a very small scale indeed. In fact, the 
scales appended to the two figures show that a length 
which represents 50,000,000 miles in fig. 17, represents 



THE PLANET MARS. 



157 



1,000,000,000 miles in fig. i8; or, in other words, the 
scale of fig. 18 is only one-twentieth of the scale of 
fig. 17. On the scale of fig. 17 the sun would be fairly 




Fig. iS. — The paths of Jupiter, Saturn, Uranus, and Neptune, around the rin^ of 
small planets. 

represented by an ordinary pin-hole ; on the scale of fig. 
18 the sun would be scarcely visible. The dots round 
the orbits show the planets' places at intervals of 10 



158 THE PLANET MARS'. 

days in fig. 17, and of 1000 days in fig. 18, starting always 
from the left side of orbit (on horizontal line through sun). 

Now looking at fig. 18 and noting how small is the 
distance of the path of Mars from the earth's path, com- 
pared with the distance of Saturn's path, we understand 
why Saturn, despite his far superior size, shines far less 
brightly in our skies than Mars does. In fact, in Octo- 
ber, 1877, the Earth and Mars were on the parts of their 
tracks which lay nearest together, that is, the parts occu- 
pying the lower right-hand corner of fig. 17 ; and turning 
to fig. 18, we perceive that the distance separating the 
two paths here is very small indeed compared with 
Saturn's distance. 

So that, when we looked at Mars and Saturn as they 
shone in conjoined splendour in our skies, in 1877, 
we saw in the bright orb of Mars the planet whose 
track lies nearest to us in that direction, whereas in 
looking at Saturn the range of view passed athwart 
the track of Mars, through the ring of asteroids, and 
past the orbit of Jupiter, before entering the wide and 
barren region which separates the orbits of the two giant 
oiembers of the solar system. 

We study Mars under much more favourable con- 
ditions than either Jupiter or Saturn. And yet, at a 
first view, the telescopic aspect of this interesting planet 
is exceedingly disappointing. Galileo, who quite easily 



THE PLANET MAkS. tj^ 

discovered the moons of Jupiter with his largest telescope, 
could barely detect with it the fact that Mars is not quite 
round at all times, but is seen sometimes in the shape of 
the moon two or three days before or after full. "' I dare 
not affirm." he wrote on December 30, 16 10, to his 
friend Castelli, '' that I can observe the phases of Mars ; 
} et, unless I mistake, I think I already perceive that he 
is not perfectly round." But even in a large telescope 
one can see very little except under very favourable con- 
ditions. It has only been by long and careful study, 
and piecing together the information obtained at various 
times, that astronomers have obtained a knowledge of 
the facts which appear in our text-books of astronomy. 
The possessor of a telescope who should expect, on 
turning the instrument towards Mars, to perceive what 
he has read in descriptions of the planet, would be con- 
siderably disappointed. 

First noticed among the features of the planet were 
two white spots of light occupying the northern and 
southern parts of his disc. These are now known to be 
regions of snow and ice, like those which surround the 
poles of our own earth. But how different the reality 
must be from what we seem to see in the telescope ! 
These two tiny white specks represent hundreds of thou- 
sands of square miles covered over with great masses of 
snow and ice, which doubtless are moved by disturbing 



!6o TilE PLANET MARS. 

forces similar to those which make our arctic regions for 
the most part impassable even for the most daring of our 
seamen. 

The snow-caps of Mars change in size as the planet 
circuits round the sun, completing his year of seasons 
(which lasts 687 of our days). They are largest in the 
winter of Mars, smallest in the Martian summer ; so that, 
as it is winter for one hemisphere when it is summer for 
the other, one of the snow-caps is larger than the other at 
the winter and summer seasons. In the same way, our 
arctic snows extend more widely during our winter, while 
the antarctic snows then retreat ; w^hereas, during our 
summer, when it is winter in the southern hemisphere, 
the antarctic snows advance and our arctic snows retreat. 

But we have still to learn why these white spots are 
known to be masses of snow. They might well from 
analogy be considered to be snows, since they behave 
like the snows of our polar regions. Yet that would be 
very different from proving them to be snow masses. I 
shall now show how this has been done, and afterwards 
describe the lands and seas of the planet, and give a 
short account of the recent interesting discovery of two 
moons attending on the planet which Tennyson had 
called the "moonless Mars.'' 

Even before the poles of Mars had been discovered, 



THE PLAXET MAR3. l6i 

observers had perceived that the planet has marks upon 
its surface. Cassini, in 1666, at Paris, found by observing 
these spots that the planet turns on its axis once in about 
twenty-four hours forty minutes. In the same year Dr. 
Hooke observed Mars. He was in doubt whether the 
planet turned once round or twice round in about twenty- 
four hours ; for with his imperfect telescope two opposite 
faces of the planet seemed so much alike that he was 
doubtful whether they really were two different faces or 
the same. Fortunately he published two pictures of the 
planet, taken on the same night in March, 1666, and we 
have been able to keep such good count of Mars's turning 
on his axis, that we know exactly how many times he has 
turned since that distant time. However, at present, we 
need not further consider the turning motion of Mars, 
but rather what the telescope has shown us about him. 
Only, let it be remembered that he has a day of about 
twenty-four hours thirty-seven minutes, and is in this 
respect much like our earth. 

Maraldi, Cassini's nephew, early in the last century 
observed several spots on Mars, and, in particular, one 
somewhat triangular dark spot, which was one of Hooke's 
markings, but more clearly seen by Maraldi. About this 
time it was seen that the darker markings have a some- 
what greenish colour; and towards the end of last 
century, or, more exactly, about a hundred years ago, 

II 



i62 THE PLANET MARS. 

the idea was maintained by Sir W. Herschel that the 
dark-greenish markings are seas, while the lighter parts 
of Mars, to which the planet owes its somewhat ruddy 
colour, are lands. Sir W. Herschel also was the first to 
show that Mars, like our earth, has seasons. It had 
been supposed by Cassini, Maraldi, and others, that the 
axis of Mars is upright to the level of the path in which 
he travels. Of course, if this were so, the light of the 
sun would always fall on the planet in the same way ; for 
the sun is in that level. But the axis, like that of our 
own earth, is bowed considerably from uprightness ; so 
that at one part of his year the sun's rays fall' more 
fully on his northern regions, and his southern regions 
are correspondingly turned away from the sun ; then it 
is summer in his northern regions, winter in his southera 
At the opposite season the reverse holds, and then winter 
prevails over his northern and summer over his southern 
regions. Midway between these two seasons, the sun's 
rays are equably distributed over both hemispheres of 
Mars, and then the days and nights are equal, and it is 
spring in that hemisphere which is passing from winter 
to summer, and autumn in the other hemisphere which 
is passing from summer to winter. All these changes 
are precisely like those which take place in the case of 
our own earth. Only, the year of Mars, and therefore 
his seasons, are longer. He takes 687 days in travelling 




> 



TBE PLANET MARS. 165 

round the sun, giving nearly 172 days, or more than five 
and a half of our months, for each season. 

Figs. 19, 20, and 21 are three views of Mars, drawn 
by Mr. Nathaniel Green, an excellent observer, who has 
paid special attention to this planet. Fig. 19 shows a 
faintly-marked sea running north and south (the upper 
part of the picture being the south, because that is the 
way in which the telescope used by astronomers inverts 
objects.) This is one of the markings which deceived 
Hooke. This picture was drawn on May 30, 1873, at 
half-past seven in the evening. The second picture was 
drawn two days earlier, at eight in the evening ; but it 
shows the planet as it would have looked on May 30 
at about a quarter past nine in the evening, by which 
time the sea running north and south had been carried 
over to the right and lost to view. But another north 
and south sea had come into view on the right. The 
third picture shows a view taken three hours later, or at 
eleven on May 28, when the planet appeared precisely 
as he would have appeared at a quarter past eleven in 
the early morning of May 31, had weather then per- 
mitted Mr. Green to continue his observations. You 
see in it the great north and south sea which Maraldi had 
noticed, the other of those two which had deceived Hooke. 

It will be seen from these drawings, which, be it 
remembered^ w^ere taken at the telescope, that it i§ 



i66 THE I'LANET MARS, 

possible from a great number of such drawings to make 
a chart of Mars, showing its lands and seas not as they 
are seen in the telescope, but as they might be laid down 
by inhabitants of Mars in a map or planisphere. This 
has been done, with gradually increasing accuracy, — first 
by Sir W. Herschel, next by Beer and Madler, then by 
Phillips, and lastly by myself (In claiming for my own 
chart greater accuracy, I am simply asserting the superior 
-completeness of the list of telescopic drawings which 
I was able to consult.) The result is shown in the 
accompanying chart (fig. 22), which presents the whole 
surface of Mars divided into lands and seas and polar 
snows, with the names attached of various observers who 
have at sundry times contributed to our knowledge of 
the planet's features. 

But now it will be asked by the thoughtful reader, how 
can any one possibly be sure that the regions called con- 
tinents and seas do really consist of land and water ? 
At any rate, the doubt might well be entertained respect- 
ing the water. For land is a wide term, including all 
kinds of rock surface, sand, earthy soil, and so forth; 
but it may seem to require proof that the substance we 
call water really exists out yonder in space, either in the 
form of snow and ice at the Martian poles, or as flowing 
water in the Martian seas, or in the vaporous form in the 
planet's air, 



THE PLAXET MAKS. r59 

Very strange, then, at fnst must the statement seem, 
that we are as sure of the existence of water in all these 
forms on Mars as if we had sent some messenger to the 
planet who had brought back for study by our chemists a 
block of Martian ice, a vessel full of Martian water, and 
a flask of Martian air saturated with aqueous vapour. 
Indeed, I do not know of any discovery effected by man 
which more strikingly displays the power of human in- 
genuity in mastering difficulties which, at a first view, 
seem altogether insuperable. When we know that a 
mass of ice as large as Great Britain would appear at 
the distance of Mars a mere bright point ; that a sea as 
large as the Mediterranean v/ould appear like a faint, 
greenish-blue, streak ; and that cloud masses such as 
would cover the whole of Europe would only present 
the appearance of a whitish glare, how hopeless seems 
the task of attempting to determine what is the real 
chemical constitution of objects thus seen ! It miglit 
well be thought that no possible explanation of the 
method used by astronomers could serve to establish 
its validity. Yet nothing can be simpler than the 
principle of the method, or more satisfactory than its 
application in this special case. 

First, let the reader rid his mind of the difficulty 
arising from the enormous distance of the celestial 
boclie§. To do this let hini note that there are some 



170 THE PLANET MARS, 

things which a body close by can tell us no more cer- 
tainly than a remote body. For instance, we are just as 
certain that Mars is a body capable of reflecting sunlight 
as we are that a cricket-ball is. We know as certainly, 
too, that the quality of Mars is such that more of the red 
of the sun's light is sent to us than of the other colours. 
For we perceive that Mars is a ruddy planet. Since 
distance in no way interferes with our perception of 
these general facts, and others like them, we need not 
necessarily find in mere distance any difficulty in the 
w^ay of recognising some other facts. All that we require 
to be shown before admitting the validity of the evidence 
is, that it is of such a kind that distance does not affect 
its qtcality, however much distance may and must affect 
the quantity of evidence. 

Now there is a means of taking the light which comes 
from a body shining either with its own or with reflected 
light, and analyzing it into its component colours. The 
spectroscope is the instrument by which this is ac- 
complished. I do not propose to describe here the 
nature of this instrument, or the details of the various 
methods in w^hich it is employed. I note only that it 
separates the rays of different colour coming from an 
object, and lays them side by side for us, — the red rays 
by themselves, the orange rays by themselves, and so 
with the yellow, green, blue, indigo, and violet. And 



THE PLANET MARS, 171 

not only are the rays of these colours set by themselves, 
but the red rays are sorted in order, from the deepest 
brown-red''' to a tint of red (the lightest) which must 
almost be called orange; the orange in order, from orange 
which must almost be called red to a tint (the lightest 
orange) which must almost be called yellow ; the yellow, 
from an almost orange yellow to a yellow just beginning 
to be tinged with green; the green, from an almost yellow 
green (the lightest) to a green which may almost be called 
blue (the darkest) ; the blue, from this tint to the begin- 
ning of the indigo ; the indigo, from this tint to the first 
rays of the violet ; and lastly the violet, through all the 
tints of this beautiful colour to a blackish-brown violet, 
where the visible spectrum ends. All these tints are 
sorted in order by the spectroscope, just as a skilful 
colourist might range in due sequence a myriad tints of 
colour. But this is only true of really white light, such 
light as comes from a glowing mass of metal burning at 
a white heat. In other cases (even when the light may 
seem white to the eye) some of the tints are found, when 
the spectroscope spreads out the colours for us, to be 
missing. And we know that this may be caused in two 
ways. Either the source of light never gave out those 

* Brown is not the right word for the tint of red w here the visible 
spectrum begins. I know, however, of no word properly expressing 
the colourt 



172 THE PLAXET MARS. 

missing lints ; or, the source of light gave them out, but 
some absorbing medium stopped them on their way 
before they reached the spectroscope with which we 
examine them. There may be cases where w^e cannot 
tell very easily which of these is the true cause. But 
sometimes we can, as the instances I have now to deal 
with will show you. 

The sun's own light shows under this method of 
spectroscopic analysis millions of tints, in fact I might 
say millions of red tints, and so forth, right through the 
spectral list of colours. But also many thousands of 
tints are wanting. Imagine a rainbow-coloured ribbon, 
the colours ranged along its length, so that the ribbon is 
black at both ends, and that from the black of one end 
the colour merges into \trs deep red, and thence by in- 
sensible gradations through orange, yellow, green, blue, 
indigo, and violet, into the black of the other end. 
Then suppose that tens of thousands of the fine threads 
which run athwart the ribbon — />., the short cross 
threads — are drawn out. Then the ribbon, laid on a 
dark background showing through the spaces where the 
threads were drawn out, would represent the solar spec- 
trum. We know then that the light of the sun's glowing 
mass either wants particular tints originally, or shines 
through vapours which prevent the free passage of rays 
of thgse colQur3. Both causes might be at work, ngt 



THE PlAl^rEt MARS, tyj 

6ne only. At present we are not concerned with this 
particular point ; but I only mention that, in reality, no 
tints are actually wanting, though some are very much 
enfeebled. 

The sun's light falling on any opaque object is re- 
flected. If the object is white, the light gives exactly 
the same spectrum, only fainter. Thus, I take a piece 
of white paper on which the sun's rays are falling, and 
examine its light with one of Browning's spectroscopes. 
I get the ordinary solar spectrum. The cold white 
paper gives me in fact a spectrum which speaks of a 
heat so intense that the most stubborn metals are not 
merely melted but vaporized in it. But this heat resides 
in the sun, not in the paper. 

Now, speaking generally, Mars also sends us sunlight, 
so that when we spread out with the spectroscope the 
rays coming from this planet, we get the solar spectrum, 
only of course very much enfeebled. But close examina- 
tion shows that other tints besides those missing from 
the solar spectrum are missing from the spectrum of 
Mars. He reflects to us the sunlight, almost as it 
reaches him, but he abstracts from it a i^w tints on his 
own account. 

When we inquire what these tints are, we find that 
they are tints which are sometimes wanting even from 
direct sunlight. When the sun sinks \Qvy low and looks 



174 THE PLANET MARS. 

like a great red ball through the moisture-laden air, his 
spectrum is not the same exactly as that of the sun 
shining high in the mid heaven. It shows other gaps 
than those corresponding to the ordinary myriads of 
missing tints. Its red colour shows indeed that some 
thing has happened to the sunlight ; but, oddly enough 
(at first sight at least), the gaps are chiefly in the red 
part of the spectrum, just what one would expect if the 
sun's light showed a want instead of an excess of ruddy 
light. The fact is, however, that the violet, indigo, and 
blue are weakened altogether, not by the mere abstraction 
of tints here and there. The red suffers under a few 
abstractions of tint, but remains on the whole little 
weakened. Now the same gaps which at such times 
appear in the spectrum of the sun are found (generally, 
if not always) in the spectrum of the planet Mars, even 
when he is shining high in the heavens, so that his light 
is 7wt at the time absorbed by the denser portions of our 
air. In fact the gaps have been seen in the spectrum of 
Mars when the planet has been shining higher in the 
heavens than the moon, whose spectrum was found on 
trial (at the time) not to show the same gaps, — as of 
course it must have done, and even more markedly, if 
the missing tints had been abstracted by our own air. 

No doubt can remain, then, that the sun's light, which 
reaches us after falling on Mars, has suffered at Mars 



THE PLANET MARS. 175 

the same absorption which our own air produces on the 
rays of the sun when he is low down. But we know 
what it is in our air which causes this absorption. It is 
the aqueous vapour. We know this from several inde- 
pendent series of researches. It was proved first by an 
American physicist, Professor Cooke of Harvard, who 
found that these lines in the red are always darker when 
the air is moister. Then by Janssen, who observed the 
spectrum of great bonfires lit at a distance of many miles, 
on the Swiss mountains, finding these same lines in the 
spectrum of the fire-light when the air was heavily laden 
with moisture. Wherefore we know that the air of Mars 
must also contain the same substance — the vapour of 
water — which, in our own air, produces these dark lines. 
We can, indeed, understand that the ruddy colour of 
Mars is in part due to this moisture, which, precisely as 
in our own air it makes the sun and moon look red, 
would, in the air of a planet, make the planet itself 
look red. 

But how much follows from the discovery that there 
is moisture in the air of Mars ! This moisture can only 
come from water in sufficient quantities. There must, 
therefore, be seas on Mars. We should be sure of this 
from the spectroscopic evidence, even without the evi- 
dence given by the telescope. We cannot doubt for a 
moment, however, knowing as we do how the telescope 



tj6 fll^ PLANE2 MARS. 

shows greenish markings on Mars, that these really arS 
the seas and oceans of the planet. And again, the white 
spots at the poles of Mars can no longer be regarded 
doubtfully. If we could not see them, but knew only, 
from the spectroscopic evidence, that Mars must have 
large seas, we should be sure that his polar regions must ' 
be covered with everlasting ice and snow, varying with 
the seasons, but always surrounding, in enormous masses, 
the poles themselves. Seeing that the telescope presents 
spots to our view which, long before the spectroscopic . 
evidence had been obtained or hoped for, had been 
regarded as analogues of our polar snows, we can now 
entertain no manner of doubt that they really are so. 

But again, recognising the presence of enormous 
masses of snow and ice around the poles of Mars, and 
knowing that not only are there wide oceans, seas, and 
lakes, but that there is an atmosphere capable of carrying 
mist and cloud, how many circumstances, corresponding 
to those which we associate with the wants of living 
creatures, present themselves to our consideration ! It 
remains that I should now consider some of these 
points. 

We have seen that Mars has water in all its forms, solid, 
liquid, and vaporous. We perceive also that his polar 
regions do not extend very much farther towards his 



THE PLANET MARS. 177 

equator than do the polar ice and snows of our own 
earth. (Of course the former do not extend so far in 
actual distance ; I refer to their extent compared with 
the globe they belong to.) It would appear then, at a 
first view, that the climate of Mars cannot be very unlike 
that of our earth. Yet this is scarcely possible. For 
Mars is so much farther than we are from the sun that 
he receives less than half as much light and heat from 
that luminary. And it is not easy to conceive that the 
deficiency can be compensated by any effects due to the 
nature of the Martian air. It is more likely by far that 
this air is much rarer than that it is much denser than 
ours. For not only can it be shown that with the same 
relative quantity of air a smaller planet v/ould have a 
smaller quantity above each square mile of its surface 
than would a larger one,''^ but the gravity at the surface 

* Suppose there are two planets A and B of equal density, of which 
A has a diameter twice as great as that of B. Then the volume of A 
is eight times greater than B's volume. So that if the volume of its 
atmosphere exceed the volume of B's air in the same degree, the 
planet A has eight times as much air as the planet B. But the sur- 
face of A is only four times as great as the surface of B ; so that 
if A had only four times as much air as B, there would be the 
same quantity of air above each square mile of A's surface as above 
each of B's surface. Since then A has eight times — not merely four 
times — as much air as B, it follows that A has twice as much air over 
each square mile of surface as B has. And similarly in all such cases, 
the general law being that the larjrer planet has more air over each 

I 



178 THE PLANET MARS. 

of the smaller planet being less, the air there is much 
less compressed by its own weight (having in fact much 
less weight), and is therefore rarer. Thus the probability 
is that the air of Mars is like that at (or even above) the 
summits of our highest mountains, where we know that 
an intense cold prevails. It is not that the sun's rays do 
not fall there with as much heating power as at the sea- 
level, for experiment shows that they fall with even 
greater power. But there is less air to be warmed and 
to retain the heat. The difference may be compared in 
fact to that between a well-watered country near the sea 
and an arid desert. The sun's rays fall as fiercely on one 
as on the other, but because there is no moisture in the 
desert to receive (after the fashion characteristic of water) 
the solar heat and retain it, the heat passes away so 
soon as the sun has set, and intense cold prevails, while 
over the well-watered region the temperature is much 
more uniform, and warm nights prevail. So is it at the 
summits of lofty mountains. The sun's rays are poured 
on them as hotly as elsewhere, but there is- little air to 
retain the moisture, so that the heat passes away almost 
as quickly as it is received, and during the night as much 
fresh snow is formed as had been melted during the day. 
And so it would certainly be with Mars, if, other things 

square mile of surface in the same degree that its diameter exceeds 
that of the other. 



THE PLANET MARS, 179 

being the same, the air were as rare as it is at the sum- 
mits of our loftiest mountains. If, as seems probable, 
the air is still rarer than this, the cold would be still 
more intense. 

It would seem, then, that either some important differ- 
ence exists, by which the Martian air is enabled to retain 
the sun's heat even more effectively than our air does 
(for the climate as indicated by the limits of the polar 
snows seems the same, though the distance from the 
sun is greater); or else there is some mistake in the 
supposition that the same general state of things prevails 
on Mars as on our own earth. 

I confess that though Professor Tyndall has shown 
clearly how the atmosphere of a more distant planet 
might make up for the deficient supply of solar heat, by 
more effectively retaining the heat, I know of nothing in 
either the telescopic or the spectroscopic evidence re- 
specting any of the planets which tends to show, or even 
renders it likely, that any such arrangement exists, — 
excepting always the peculiarity in Mars's case which we 
are now endeavouring to explain. Insomuch that should 
any other explanation of the difficulty be suggested, and 
appear to have weight in its favour, I apprehend that the 
mere possibility of an atmospheric arrangement, such as 
has been suggested, should not prevent-our admitting 
this other explanation. 



l8o THE PLANET MARS. 

I am inclined to think that there is such an explana- 
tion. It seems to me that there are good reasons for 
regarding Mars as a planet which has passed to a much 
later stage of planetary life than that through which our 
earth is now passing, and that in this circumstance some 
of the peculiarities of his appearance find their explana- 
tion. As a planet outside the earth, Mars must probably 
be regarded as one formed somewhat before the earth. 
As a much smaller planet, he would be not only less 
heated when first found (whatever theory of planetary 
formation we adopt), but would also have parted much 
more rapidly (relatively) with his heat, according to the 
same law which makes a small mass of metal cool more 
quickly than a large one. If he has a rarer atmosphere 
he would be a colder planet on that account also. Being 
also remoter from the sun, he receives less heat from 
that orb, and we thus have a fourth reason for regarding 
Mars as a much colder planet than our earth, both as to 
inherent heat and as to heat received from without. It 
seems to me that we m.ay in this consideration find the 
real meaning of the comparatively limited extension of 
the Martian snows. It has been well pointed out by 
Professor Tyndall that for the formation of great glacial 
masses, not great cold only, but great heat also is re^ 
quired. The snows which fall on mountain slopes, to be 
compacted into ice and afterwards to form great glaciers, 



THE PLANET MARS, l8i 

\vere raised into the air by the sun's heat. Every ice 
particle represents the action of that heat upon the 
particles of water at the surface of ocean, sea, or lake, or 
of wet soil. If the sun's heat suddenly died out, there 
would prevail an intense cold, and the snows and ice 
now existing would assuredly remain. The waters also 
of the earth \7ould congeal. But no new snows would 
fall. The congealed seas viewed from some remote 
planet would appear unchanged. For they would not 
be covered with snow and broken ice, nor therefore 
white ; but would consist of pure ice throughout, retain- 
ing the partial transparency and greenish colour of deep- 
sea water. No winds would disturb the surface of the 
frozen seas, for winds have their origin in heat, and with 
the death of the solar heat the winds would utterly die 
out also. 

If we are to choose between these two explanations,— 
one that the snows and ice have not the great range we 
should expect, because the temperature is somehow 
raised despite Mars's greater distance to the same tem- 
perature which we experience, and the other that it 
is not heat but cold which diminishes the quantity of 
Martian snow, I conceive that there is every reason the 
Case admits of for accepting the latter instead of the 
former explanation. As extreme cold would certainly 
prevent glacial masses from being very large and deep, 



i82 THE PLANET MARS. 

simply because the stores whence the ice was gathered 
would be lesSj the snow caps of a very cold planet would 
vary as readily with varying seasons as those of a planet 
like our earth. For though less heat would be poured 
upon them with the returning summer, less heat would 
be required to melt away their outskirts. 

I think we may fairly regard Mars as in all probability 
a somewhat old and decrepit planet. He is not abso- 
lutely dead, like our own moon, where we see neither 
seas nor clouds, neither snow nor ice, no effects, in fine, 
of either heat or cold. But I think he has passed far on 
the road towards planetary death,— that is, towards that 
stage of a planet's existence when at least the higher 
forms of hfe can no longer exist upon the planet's 
surface. 

There is one peculiarity of the planet's appearance 
which seems strikingly to accord with this view that Mars 
holds a position intermediate between that of our earth 
and the moon, — as indeed we might fairly expect from 
his intermediate proportions. The seas of our earth 
cover nearly three-quarters of her entire globe. The 
moon has no visible water on her surface. If we 
examine the chart of Mars at page 167, we see that 
the seas and oceans of the planet are much smaller 
(relatively as well as actually) than are the seas of our 
own earth. I have carefully estimated their relative 



THE PLANET MARS. 1 83 

extent in the following simple but effective way. I drew 
a chart such as the above-mentioned, but on a projection 
of my own invention, in which equal surfaces on a globe 
are represented by equal surfaces on the planisphere. 
Then I cut out with a pair of scissors the parts represent- 
ing land and the parts representing water (leaving the 
polar parts as doubtful), and carefully weighed these in a 
delicate balance. I found that they were almost exactly 
equal : whatever preponderance there was seemed to be 
in favour of the land. . Thus, if we assume that, when in 
the same stage of planetary existence. Mars had as great 
a relative extent of water surface as our earth, or that 
about -Yi-Q of the surface of Mars were originally water, 
we should have to admit that the water had so far been 
withdrawn into the planet's interior as to diminish the 
v/ater- surface by -^^ (for there are now barely 1^). At 
a very fair assumption as to the slopes of the Martian 
sea-bottoms, it would follow that more than half the 
Martian water originally existing above the surface had 
been withdrawn into the interior, as the planet^s mass 
gradually cooled. 

I am aware the assumption above mentioned is in 
itself somewhat daring, and is not supported by direct 
evidence. But, since we have very strong reasons for 
considering that the moon once had seas, which have 
been withdrawn in the way suggested, and since Mars 



I §4 fllE PLANET MARS. 

unquestionably holds a position midway between the 
earth and moon as to size and presumably as to age,"' it 
seems not unreasonable to find in the character of her 
seas, — less extended relatively than the earth's, but, un- 
like the moon's, still existing, — the evidence that she has 
gone partially through the process through which the 
moon has long since passed completely. ^JH 

I think it very likely that the recent discovery of two 
Martian satellites will lead many to look with more dis- 
favour than ever on the idea that Mars may not at 
present be the abode of life. For moons seem so mani- 
festly convenient additions to a planet^s surroundings, as 
light-givers, time-measurers, and tide-rulers, that many 
will regard the mere fact that these conveniences exist as 
proof positive that they are at this present time subserving 
the purposes which they are capable of subserving. I 
would point out, however, that our own moon must have 
existed for ages before any living creatures, far less any 
reasoning beings, could profit by her light, or by the 
regularity of her motions, or by her action in swaying the 
waters of ocean. And doubtless she will continue to 
exist for ages after all life shall have passed away from the 

* By age here I do not mean absolute age, but relative age. I 
speak of Mars and the Moon as older than the earth in the same 
sense that I should speak of a fly in autumn as older than a five-year- 
old raven. 



The planet ji/jps. t§5 

earth. Again, there can be no question that our earth 
would present a most attractive scene if she were viewed 
from the moon, and would be a most useful ornament of 
the lunar skies. Yet we have every reason to believe 
that there is not a living creature on the moon at present 
to profit by her light. The case may w^ell be the same 
(apart from the actual evidence that it is the same) with 
Mars. His satellites may long since have served most 
useful purposes to his inhabitants; but it by no means 
follows that because if there were inhabitants on Mars 
now the same purposes would still be subserved, therefore 
there are inhabitants there. 

Let us, however, without considering the question 
whether the satellites of Mars serve such special purposes 
for creatures living on the planet, consider briefly the 
history of their discovery, their nature, and the laws of 
their motion around the planet. 

Astronomers had long examined the neighbourhood of 
Mars with very powerful telescopes, in the hope of disco- 
vering Martian moons. But the hope had so thoroughly 
been abandoned for many years that the planet had come 
to be known as "moonless Mars.'' The construction, how- 
ever, of the fine telescope which has been mounted at 
AVashington, with an object-glass twenty-six inches in 
diameter, caused at least American astronomers to hope 
that after all a Martian moon or two might be discovered. 



1 86 THE PLANET MARS. 

Taking advantage of the exceptionally favourable oppor- 
tunity presented during the planet's close approach to 
our earth in the autumn of 1877, Prof. Asaph Hall, of the 
Washington Observatory, paid special attention to the 
search for Martian moons. At last, on August 16, 1877, 
he detected close by the planet a faint point of light, 
which he was unable to examine further at the time (to 
see if it behaved as a satellite, or as one of the fixed stars). 
But on the i8th he saw it again, and determined its nature. 
He also saw another still fainter point of light closer to 
the planet ; and subsequent observations shewed that this 
object also was a satellite. During the next few weeks 
both the moons were observed as closely as possible, in 
fact, whenever weather permitted, and the result is that 
we now know the true nature of their paths. 

In fig. 23 these paths are shown as they appeared in 
1877. Of course the paths themselves are not seen; 
but if the satellites left behind them a fine train or wake 
of light, the shape of this train would be as shown in fig. 
23. The satellites themselves could not be shown at all 
in a picture on so small a scale — the diameter of either 
would certainly be less than the cross-breadth of the fine 
elliptical line representing its track. The size of the 
planet is correctly indicated, and the true pose of the 
planet in 1877 is shown in the figure, his southern 
pole being somewhat bowed towards the earth. This is 



THE PLANET MARS, 1S7 

the uppermost pole ; for the figure represents the planet 
and his satellites' orbits as they would appear in an as- 
tronomical telescope, which inverts objects. 

The outer satellite is probably not more than ten 
miles or so in diameter, the inner one, perhaps, the 
same ; but neither can be measured. In the most 
powerful telescopes they appear as mere points of light. 




Fi^- 23. — Mars and the paths of the Martian satelUtes as at present situated. 

Nor is it easy to determine, from their lustre, or rather 
from their faintness, their true dimensions ; for we can- 
not compare them directly in this respect with objects of 
known size, because their visibility is partly affected by 
the proximity of the planet, whose overpowering light 
dims their feeble ra}'^. This remark applies with special 
force to the inner satellite. 

The distance of the outer satellite from Mars's centre 



18B THE PLANET MARS, 

is about 14,300 miles, from Mars's surface about 1 2,66(5 
miles. The inner travels at a distance of about 5,750 
miles from the centre, and about 3,450 miles from the 
surface of Mars. 

The motions of the satellites as seen from Mars must 
oe very different from those of our own moon. Thus, 
our moon moves so slowly among the stars that she 
requires nearly an hour to traverse a distance equal to 
her own apparent diameter. The outer moon of Mars 
traverses a similar distance — that is, not her own ap- 
parent diameter, but an arc on the stellar heavens equal 
to our moon's apparent diameter — in about two and a 
half minutes, while the inner moon moves so rapidly as 
to traverse the same distance in about forty seconds. 
To both moons, therefore, but to the inner in particular, 
Job's description of our moon as ^Svalking in brightness " 
would seem singularly applicable, so far at least as the 
rapidity of their motions is concerned. Their brightness, 
however, cannot be -comparable to our moon's. For 
notwithstanding their much greater proximity, it is easily 
shown that they must present much smaller discs, and 
being illuminated by a more distant sun, their discs can- 
not shine so brightly as our moon's. That is, not only 
are the discs smaller, but their intrinsic brightness is less. 
Assuming the outer moon to be ten miles, the inner 
fifteen miles in diameter, it is easily shown that the two 



THE riANET MARS, 189 

together, if full at the same time, can hardly give one- 
twelfth as much light to Martians as our moon gives to 
us. 

Yet there can be no doubt that the Martian moons must 
be (or have been) most useful additions to the Martian 
skies. They do not give a useful measure of time inter- 
mediate in length between the day and the year, as our 
moon does ; for the outer travels round the planet in 
about thirty and a quarter hours, the inner in about seven 
and a half hours. Nor can they exert an influence upon 
the Martian seas corresponding to that exerted by our 
own moon in generating the lunar tidal wave. But their 
motions must serve usefully to indicate the progress of 
time, both by night and by day, for they must be 
visible by day unless very close to the sun. They must 
be even more useful than our moon in indicating the 
longitude of ships at sea, seeing that the accuracy with 
which a moon indicates longitude is directly proportional 
to her velocity of motion among the stars. 

I have said that there does not seem to be any valid 
reason for considering that now is the accepted time with 
these moons ; their services may have been of immense 
value in long past ages, and now be valueless for want of 
any creatures to be benefited by them. But those who 
not only believe that no object in nature was made with- 
out some special purpose, but that we are able to assign 



190 THE PLANET MARS. 

to each object its original purpose, should be well satisfied 
if they find reason for believing that, during millions 
of years long, long ago, the moons lately discovered by 
our astronomers were measuring time for past races of 
Martians, swaying tides in wider seas than those which 
now lave the shores of Martian continents, and enabling 
Martian travellers to guide their course over the trackless 
ocean and arid desert with far greater safety than can our 
voyagers by sea and land despite all the advances of 
modern science. 



X. 



THE PLANET JUPITER. 



J^^^^WO or three years ago I had occasion to con- 
sider in the Day of Rest the giant planet 
Jupiter, the largest and most massive of 
all the bodies circling around the sun. I then pre- 
sented a new theory respecting Jupiter's condition, to 
which I had been led in 1869, when I was visiting other 
worlds than ours. Since then, in fact within the last few 
months, observations have been made which place the 
new theory on a somewhat firm basis; and I propose 
now briefly to reconsider the subject in the Hght of these 
latest observations. 

In the first place I would call the reader's attention to 
the way in which modern science has altered our ideas 
respecting time as well as space, though the change has 
only been noticed specially as it affects space. In former 
ages men regarded the region pi space over which they 



192 THE PLANET 7UFITER, 

in some sense had rule as very extensive indeed. This 
earth was the most important body in the universe, all 
others being not only made for the service of the earth, 
but being in all respects, in size, in range, and so forth, 
altogether subordinate to it. Step by step men passed 
from this to an entirely different conception of our earth's 
position in space. Shown first to be a globe within the 
domain of the heavenly bodies, then to be a globe sub- 
ordinate to the sun, then to be a member of one family 
among thousands each with its ruling sun, then to belong 
to a galaxy of suns which is but one among myriads of 
millions of such galaxies, and lastly shown to the eye of 
reason, though not to direct observation, as belonging to 
a galaxy of galaxies itself but one among millions of the 
same order, which in turn belong to higher and higher 
orders endlessly, the earth has come to be regarded, 
despite its importance to ourselves, as but a point in 
space. The minutest particle by which a mathematician 
might attempt to picture the conception of a mathema- 
tical point, comparing that particle with any near object 
however large, a house, a mountain, the earth itself, 
would be but the grossest representation of a point, by 
comparison with the massive earth, when she is con- 
sidered with reference to the universe of the fixed stars 
or rather to that portion of the universe, itself but a point 
in space, over which the survey of the astronomer extends. 



^itE PLANET ytfPITEk, 103 

All this has been admitted. Men have fully learned to 
tecognise, though they are quite unable to conceive, the 
utter minuteness, one may say the evanescence, of their 
abode in space. 

But along with the extension of our ideas respecting 
space, a corresponding extension has been made, or 
should have been made, in our conceptions respecting 
time. We have learned to recognise the time during 
which our earth has been and will be a fit abode for living 
creatures as exceedingly short compared with the time 
during which she was being fashioned into fitness for that 
purpose, and with the seons of seons to follow, after life 
has disappeared from her surface. This, however, is but 
one step towards the eternities to which modern science 
points. The earth is but one of many bodies of a 
System ; and though it has been the custom to regard the 
birth of that system as if it had been effected, if one may 
so speak, in a single continuous effort (lasting milUons of 
millions of years, mayhap, but bringing all the planets 
and their central siin simultaneously into fitness for their 
purpose), there is no reason whatever for supposing this 
to have been really the case, while there are many reasons 
for regarding it as utterly unlikely. It seems as though 
men could not divest themselves of the idea that our 
earth's history is the history of the solar system and of 
the universe. Precisely a§ children can hardly be 

13 



194 THE PLANET yUPITER. 

brought to understand^ for a long time, what history 
really means, how generation after generation of their 
own race has passed away, and how their own race has 
succeeded countless others, so science, still young, seems 
scarcely to appreciate the real meaning of its own dis- 
coveries. It follows directly from these that world after 
world like our earth, in this our own system or among 
the millions peopling space, has had its day, and that 
the systems themselves, on which such worlds attend, are 
but the existent representatives of their order, and suc- 
ceed countless other systems which have long since served 
their purpose. 

Yet, strangely enough, students of science continue for 
the most part to speak of other worlds, and other suns, 
and other systems, as though this present era, this " bank 
and shoal of time," were the sole period to which to refer 
in considering the condition of those worlds and suns 
and systems. It does not seem to occur to them that, — 
not possibly or probably, but most certainly,— myriads 
among the celestial bodies must be passing through 
stages preceding those which are compatible with the 
existence or support of life, while myriads of others must 
long since have passed that stage. And thus ideas 
appear strange and fanciful to them which, rightly ap- 
prehended, are alone in strict accordance with analogy. 
To consider Jupiter or Saturn as in the extreme youth of 



The planet jupiter, 195 

planetary existence, still glowing with such heat as per- 
vaded the whole frame of our earth before she became a 
habitable world, still enveloped in cloud masses contain- 
ing within them the very oceans of those future worlds, 
all this is regarded as fanciful and sensational. Yet those 
who so regard such theories do not hesitate to admit that 
every planet must once in its life pass through the fiery 
stage of planetary existence, nor are they prepared to 
show any reason why the stage must be regarded as past 
in the case of every planet or even of most of the planets. 
Seeing that, on the other hand, there are abundant 
reasons for believing that planets differ very widely as 
regards the duration of the various stages of their life, 
and that our earth is by no means one of the longest 
lived, we may very fairly expect to find among the 
planets some which are very much younger than our 
earth, — not younger, it will be understood, in years, 
but younger in the sense of being less advanced in 
development. When we further find that all the evi- 
dence accords with this view, we may regard it as the 
one to which true science points. 

All that we know about the processes through which 
our earth has passed suggests the probability, I will even 
say the certainty, that planets so much larger than she 
is as are Jupiter and Saturn must require much longer 
periods for every one of those processes. A vast mass 



196 THE PLANET ^UFITEk, 

like Jupiter would not cool down from the temperature 
which our earth possessed when her surface was molten 
to that which she at present possesses in the same time 
as the earth, but in a period many times longer. 
- Supposing Bischoff to be right in assigning 340,000,000 
years to that era of our earth^s past, I have calculated 
that Jupiter would require about seven times and Saturn 
nearly five times as long, or about 2,380,000,000 and 
1,500,000,000 years respectively, and by these respec- 
tive periods would they be behind the earth as respects 
this stage of development. Suppose, however, on the 
other hand, that Bischoff has greatly overrated the length 
of that era— and I must confess that experiments on 
the cooling of small masses of rock, such as he dealt 
with, seem to afford very unsatisfactory evidence respect- 
ing the cooling of a great globe like our earth. Say that 
instead of 340,000,000 years we must assign but a tenth 
part of that time to the era in question. Even then 
we find for the corresponding era of Jupiter's exist- 
ence about 238,000,000 years, and for that of Saturn^s 
150,000,000 years, or in one case more than 200,000,000 
years longer, in the other more than 110,000,000 years 
longer than in our earth's case. 

This relates to but one era only of our earth's past. 
That era was preceded by others which are usually 
considered to have lasted much longer. The earth, 



THE PLANET JUPITER. 197 

according to the nebular theory of Laplace, was once a 
mighty ring surrounding the sun, and had to contract 
into globe form, a process requiring many millions of 
years. When first formed into a globe she was vaporous, 
and had to contract — forming the moon in so doing — 
until she became a mass, first of liquid, then of plastic 
half solid matter, glowing with fire and covered with 
tracts of fluent heat. Here was another stage of her past 
existence, requiring probably many hundreds of millions 
of years. Jupiter and Saturn had to pass through similar 
stages of development, and required many times as many 
years for each of them. Is it then reasonable to suppose 
that they have arrived at the same stage of development 
as our earth, or indeed as each other. 

Supposing for a moment that we were fully assured 
that Jupiter and Saturn had separate existence, hundreds 
of millions of years before our earth had been separated 
from the great glowing mass of vapour formerly con- 
stituting the solar system, and that having this enor- 
mous start, so to speak, they need not necessarily be 
regarded as now very greatly in arrear as respects devel- 
opment, or might even be in advance of the earth, it is 
altogether improbable that either of them, and far more 
improbable that both of them, are passing through 
precisely the same stage of development. If we knew 
Qnly of two ships, that one had to trayel frgm New York 



198 THE PLANET JUPITER^ 

to London, and another from Canton to Liverpool, some 
time during the year, and that the one which had to 
make the longer journey was likely to start several weeks 
before the other, would it not be rather unsafe to con- 
clude, when the former had entered the mouth of the 
Thames, that in all probability the other was sailing up 
the Mersey? Yet something like this, or in reality 
much wilder than this, is the reasoning which permits 
the student of science to believe, independently of 
the evidence, or altogether against all evidence, that 
Jupiter and Saturn are necessarily passing through the 
very stage of planetary existence through which the one 
planet we know much about is passing. 

It seems to me that the student of science should be 
prepared to widen his conceptions of time even as he has 
been compelled to widen his conceptions of space. As 
he knows that the planets are not, as was once supposed, 
mere attendants upon our earth and belonging to her 
special domain in space, so should he understand that 
neither do the other planets appertain of necessity to the 
domain of time in which our earth's existence has been 
cast, or only do so in the same sense that like her they 
occupy a certain domain in space, not her domain, but 
the sun's. Their history in time, like hers, doubtless 
belongs to the history of the solar system, but the dura- 
tion of that system etiormously surpasses the duration of 



THE PLANET JUPITER. 199 

the earth as a planet, and immeasurably surpasses the 
duration of that particular stage of life through which 
she is now passing. 

Prepared thus to view the other planets independently 
of preconceived ideas as to their resemblance to our own 
earth, we shall not find much occasion to hesitate, I 
think, in accepting the conclusion that Jupiter is a very 
much younger planet. 

We have seen already that the enormous mass of 
Jupiter, surpassing that of our earth 340 times, is sug- 
gestive of the enormous duration of every stage of his 
existence, and therefore of his present extreme youth. 
His bulk yet more enormously exceeds that of our earth, 
as, according to the best measurements, no less than 1230 
globes, as large as our earth, might be formed out of the 
mighty volume of the prince of planets. In this superi» 
ority of bulk, nearly four times greater than his vast 
superiority of mass, we find the first direct evidence from 
observation in favour of the theory that Jupiter is still 
intensely hot. How can a mass so vast, possessing an 
attractive power in its own substance so great that, under 
similar conditions, it should be compressed to a far 
greater degree than our earth, and be, therefore, con- 
siderably more dense, come to be considerably rarer? 
We no longer believe that there is any great diversity of 
material throughout the solar system. We cannot sup- 



200 THE PLANET JUPITER, 

pose, as Whewell once invited us to do, that Jupiter 
consists wholly or almost wholly of water. Nor can we 
imagine that any material much lighter than ordinary 
rocks constitutes the chief portion of his bulk. We are, 
to all intents and purposes, forced to believe that the 
contractive effect due to his mighty attractive energy is 
counteracted by some other force. Nor can we hesitate, 
since this is admitted, to look for the resisting force in the 
expansive effects due to heat. We know that in the case 
of the sun, where a much mightier contractive power is at 
work, a much more intense heat so resists it that the sun 
has a mean density no greater than Jupiter's. We have 
every reason, then, which bulk and mass can supply, to 
believe that Jupiter is far hotter than the earth — that 
in fact, as the sun, exceeding Jupiter more than looo 
times in volume, is many times hotter than he is, so 
Jupiter, exceeding our earth 1200 times in volume, is 
very much hotter than the earth. 

But when we consider the aspect of Jupiter we find 
that similar reasoning applies to his atmosphere. The 
telescope shows Jupiter as an orb continually varying in 
aspect, so as to assure us that we do not see his real 
surface. The variable envelope we do see presents, 
further, all the appearance of being laden with enor- 
mously deep clouds. The figure (24) shows the planet as 
seen by Herr Lohse gn February 5, 1872, and server 



TEE PLANET yUPIlER. 20l 

to illustrate the rounded clouds often seen in Jupiter's 
equatorial zone, as though floating in the deep atmos- 
phere there. Although rounded clouds such as these 
are not constantly present, they are very often seen ; 
their appearance, even on a few occasions only, would 
suffice for the argument I now propose to draw from 




Fig. 24. — The Planet Jupiter. 

them. It is impossible to regard them as flat round 
clouds. Manifestly they are globular. Now they may 
not be quite as deep as they are long, or even broad, 
but supposing them only half as deep as they are broad, 
that would correspond to much more than a third of 
the diameter of our earth, shown in the same picture. 
The atmosphere in which they float would necessarily 



202 THE PLANET JUPITER, 

be deeper still, but that depth alone would be about 
3,000 miles. Now an atmosphere 3,000 miles deep 
under the tremendous attraction of Jupiter's mass would 
be compressed near its base to a density many times 
exceeding that of the densest solids if (which of course 
is impossible) it could remain in the gaseous form with 
such density. The fact, then, that an atmosphere, cer- 
tainly gaseous, exists around Jupiter to this enormous 
depth at least, proves to demonstration that there must 
be some power resisting its attractive energy ; and again, 
we have little choice but to admit that that power is no 
other than the planet's intense heat. 

As we extend our scrutiny into the evidence from 
direct observation, we find still other proofs independent 
of those just considered. One proof alone, be it re- 
membered, is all that is required, but it will be found 
that there are many. 

We have found reasons for believing that the planet 
Jupiter is expanded by heat in such sort that the 
contractive or condensing power of his own mighty 
attractive energy is overcome. We know certainly that, 
regarding the planet we see as a whole, its globe is 
of very small density. We have every reason to be- 
lieve that it is made of the same materials, speaking 
generally, as our earth. We know that its mass as 



THE PLACET JUPITER, 203 

a whole possesses many times the gravitating power 
of our earth's mass. It is highly probable, therefore, 
that the condition of its substance is very different 
from that of our earth's substance. And as we know 
of no cause save heat which could keep the planet in 
this state, it is altogether probable that the planet is 
extremely hot. The argument, be it noticed, is inde- 
pendent of that based on the probability that Jupiter, 
owing to his enormous mass, has not cooled nearly so 
much as our earth has. 

We then noticed another very powerful argument, 
similar in kind, but also quite independent, derived 
from the aspect of the planet. Jupiter's appearance 
indicates clearly that he has a deep cloud-laden atmos- 
phere, and we know that such an atmosphere, if of the 
same temperature as our earth's, would be compressed 
enormously, whereas the observed mobility of Jupiter's 
cloud-envelope, and other circumstances, indicate that 
this enormous compression does not exist. We infer, 
then, that some cause is at w^ork expanding the atmos- 
phere ; and w^e know of no other cause but heat which 
could do so effectively. 

But now let us consider certain details which the 
telescope has brought to our knowledge. 

In the first place, a number of circumstances indicate 
a tremendous activity in that deep.cbud-laden .air, 



204 1^^^ PLANET JUPITER. 

The cloud-belts sometimes change remarkably in 
appearance and shape in a very short time. Mr. Webb, 
in his excellent little treatise, " Celestial Objects for 
Common Telescopes,'' gives instances from the observa- 
tions of South, which I here translate into non -technical 
terms: — On June 3, 1839, at about nine in the evening. 
South saw with his large telescope, just below the 
principal belt of Jupiter, a spot of enormous size. It 
was dark, and therefore probably represented an open- 
ing in a great cloud-layer by which a lower or inner 
layer was brought into view. (For though the planet's 
real globe may be so intensely hot as to emit a great 
deal of light, it is probable that most of the light so 
emitted is concealed by the enwrapping cloud masses, 
and that the greater part of the light we receive from 
the planet is reflected sunlight ; so that the inner cloud- 
layers would be the darker.) South estimated this spot 
as about 20,000 miles in diameter. " I showed it," he 
says, "to some gentlemen who were present; its enor- 
mous extent was such that on my wishing to have a 
portrait of it, one of the gentlemen, who was a good 
draughtsman, kindly undertook to draw me one ; whilst 
I, on the other hand, extremely desirous that its actual 
magnitude should not rest on estimation, proposed, on 
account of the scandalous unsteadiness of the large 
instrument, to measure it with my five -feet telescope." 



fkE PLANET yUPlTEk, ios 

"Having obtained for my companion the necessary 
drawing instruments, I went to work, he preparing him- 
self to commence his." But on looking into the tele- 
scope, South was astonished to find that the large dark 
spot, except at its eastern and \vestern edges, had be- 
come much whiter than any of the other parts of the 
planet ; and thirty-four minutes after these observations 
had commenced, "these'' [query three?] "miserable 
scraps were the only remains of a spot which but a few 
minutes before had extended over at least 20,000 miles, 
—or two and a half times the diameter of the earth." 

The cloud envelope, then, of Jupiter is certainly not 
in a state of quiescence. Of course we need not suppose 
that winds had carried cloud masses athwart the tre- 
mendous opening seen by South. That would imply 
a motion of 10,000 miles in the half-hour or so of 
observation, — supposing contrary winds to have rushed 
towards the centre, — or double that velocity if the entire 
breadth of the spot had been traversed in that time. 
A velocity of 20,000 miles, and still more of 40,000 
miles per hour, may fairly be regarded as incredible. 
It would exceed more than a hundred-fold (taking the 
least number) the velocity of our most tremendous 
hurricanes. And although the solar hurricanes would 
seem to have a velocity, at times, of 300,000 or 400,000 
miles per hour, we have no reason for supposing that 



2o6 THE PLANET JUPITER, 

winds of tens of thousands of miles per hour could be 
raised in the atmosphere of Jupiter. As I have said, 
however, it is not necessary to suppose this. We may 
conceive that clouds had formed very rapidly at the 
higher elevation where before they had been wanting. 
Clouds may form as readily and quickly over an area 
a thousand miles across as over an area two or three 
miles across. Indeed Webb, referring to such changes 
as South witnessed, says that Sir J. Herschel once 
observed a cloud-bank in our own air, which formed 
so rapidly that it crossed the sky at the rate of 300 
miles an hour, not moving, of course, at that rate, but 
being formed along different parts of its apparent pro- 
gress almost simultaneously, so as to appear to travel 
with this enormous velocity. 

But now I wish the reader specially to notice hovv^ 
this observation of South's may serve to explain another, 
equally remarkable and at first sight far more perplex- 
ing; and how, when the two observations are brought 
together, a very singular piece of information is obtained 
respecting Jupiter's cloud-envelope. 

Let a ^, fig. 25, represent the great dark space seen 
by South, just below the principal belt, and let us suppose 
the planet turned round until this dark space, or rather 
this opening in the planet's outer cloud-envelope, is 
II brought to the edge as at a r d^ fig. 26. Then this 



THE PLANET yUPiTER. ^oj 

opening would really cause a depression in the planet's 
outline at d c, the shaded part being depressed. The 
depression might not be observable in any ordinary 
telescope. For at the edge of Jupiter the features of 




Fig. 25. Fig. 26. 

the belt are generally lost, and the outline is at all times 
smoothed in appearance by that peculiarity of vision 
which makes all bright objects seen on a dark back- 
ground appear somewhat larger than they actually are. 
(This is really due to a fringing, as it were, of the image 
on the retina of the eye.) But though the depression 
might not be recognisable, it would exist, and, as we shall 
presently see, it might be detected in another way than 
by being actually seen. When the clouds formed which 
concealed the spot, — -we do not know how quickly, but 
certainly in less than thirty-four minutes,— the depression, 
had the spot been at the edge, would have been removed. 
This change, however, like the existence of the depression, 
would doubtless not have been discernible by ordinary 
vision. 




2o8 ^^f^iMd^ET ^uPiTeA 



Now^ let us consider the second observation mentioned 

above.- ESTABLISHED ,-75, ""| 

On Thursday) June 26, 1828, the secong satellite of 
Jupiter w^s ^foj^t to make a passage across the planet's 
face. It was^i^^rvTO^fiT^^fbre this passage or transit 
began, in the position shown in fig. 27 by the late Admiral 
Smyth. He was using an excellent telescope. It gradually 
made its entry, looking for a few minutes like a small 
white mountain on the edge of the planet, and finally 




Fig. 27. Fig. 28. Fig. 29. 

disappeared. The reader must understand that the moon 
was not hiding itself behind the planet, but was on this 
side of it, and simply lost to view because its brightness 
was the same, or very nearly the same, as that of the 
planet^s edge. (Its place is show^n in fig. 28, but of course 
the little dark ring was not so seen.) ^^ At least 12 or 13 
minutes must have elapsed," says Smyth, ^^ when, acci- 
dentally turning to Jupiter again, to my astonishment 1 
perceived the same satellite outside the disc,'^ as shown 
in fig. 29. It remained visible there for at least four 



rilE PLANET JUPITER. 209 

minutes, and then suddenly vanished. To show that 
the observation was not due to any local or personal 
peculiarity, it is only necessary to mention that two 
other astronomers, Mr. Maclear at Biggleswade, and Dr. 
Pearson at South Kilworth, observed the same extraor- 
dinary behaviour of Jupiter's second satellite. The three 
telescopes are thus described by Admiral Smyth, — • 

Mr. Maclear's, 3^ inches in opening, 3.^ feet long ; 
Dr. Pearson's 6f inches in opening, 12 feet long ; 
Adm. Smyth's 3 J inches in opening, 5 feet long ; 

all good observing telescopes. Now, of course, the 
satelHte did not really stop. Nothing short of a miracle 
could have stopped the satellite, or, if the satellite could 
have stopped, have set it travelling on again as usual. 
For the satellite did not lose one mile, or change its 
velocity by the thousandth part of a mile per hour or even 
per annum. 

But suppose such a change had taken place at the edge 
of Jupiter as we have seen would certainly have taken 
place there if the changes affecting the spot which South 
saw had occurred to a region at the edge, as in fig. 26, 
instead of the middle, as in fig. 25. Then Smyth's 
observation would be perfectly explained. We require, 
indeed, to suppose the change occurring in a different 
order, the outer cloud-layer being in the first instance 
well-developed and very rapidly becoming dissipated, so 

14 



210 IHE PLANET JUPITER, 

that the outline which had at first been at its usual level, 
was very rapidly depressed to the inner xloud-layer. 
But, of course, if the rapid formation of clouds by con 
densation can occur on Jupiter, so also can the rapid 
dissipation occur, especially at that particular part where 
Smyth saw the satellite behave so strangely. For that 
part is being carried, by the planet's swift rotation, into 
sunlight, and the extra heat to which it is thus exposed 
might readily effect the dissipation of widely extended 
cloud strata, supposing the temperature near that critical 
value at which clouds form or are dissipated. 

Here, then, is an explanation of a phenomenon which 
otherwise seems utterly inexplicable. The explanation 
requires only that a process like one which has been 
observed to occur on Jupiter's disc should occur at a 
part of his surface forming at the moment a portion 
of his outline. If we had never known of such changes 
as South and other observers have noted in the markings 
of Jupiter, we should be compelled by Smyth's observa- 
tion to admit their possibility. If we had never known 
of Smyth's observation we should be compelled by 
South's to admit that such a change of outline as is 
indicated by Smyth's observation must be possible, — 
must, in fact, occur whenever cloud-masses form or are 
dissipated over wide areas at the apparent edge of the 
planet. When we have both forms of evidence it seems 



THE PLANET JUPITER, 21 1 

altogether unreasonable to entertain any further doubt 
on this point. 

But Smyth's observation, thus interpreted, indicates 
an enormous distance between the outer and inner cloud- 
layers which formed the planet's edge near the satellite 
in figs. 28 and 29 respectively. I find after making every 
possible allowance for errors in his estimate of time, not 
taken it would seem from his observatory clock, that the 
distance separating these cloud-layers cannot have been 
less than 3,500 miles, or not far from half the diameter 
of our earth. It is the startling nature of this result 
which perhaps deters many from accepting the explana- 
tion of Smyth's observation here advanced. But there 
is no other explanation. The satellite cannot have 
stopped in its course; Jupiter cannot have shifted his 
place bodily ; the satellite was on this side of the planet, 
— therefore no effects of the planet's atmosphere on the 
line of sight from the planet can help us ; three observers 
at different stations saw the phenomenon, — therefore 
neither effects of our earth's atmosphere nor personal 
peculiarities can account for the strange phenomenon. 
" Explanation is set at defiance," says Webb ; '' demon- 
strably neither in the atmosphere of the earth nor 
Jupiter, where and what could have been the cause?" 
The explanation I have advanced is the only possible 
answer to this cfuestion. 



2X2 THE PLANET JUPITER, 

I might occupy twenty times the space here available 
to me in detaiUng various other phenomena all pointing 
in the same way, — that is, all tending to show that Jupiter 
is a planet glowing with intense heat, surrounded by a 
deep cloud-laden atmosphere, intensely hot in its lower 
porllons, but not necessarily so in the parts we see, and 
undergoing changes (consequences of heat) of a stupen- 
dous nature, such as the small heat of the remote sun, 
which shines on Jupiter with less than the 27th part of 
the heat we receive, could not by any possibility produce. 
But partly because space v/ill not permit, partly because 
most of these phenomena have been described in my 
^^Ovbs Around Us,'' and ^^ Other Worlds," I content 
myself by describing a singular observation recently 
made, which, v/ith South's and Smyth's, seems to place 
the theory I have advanced beyond the possibility of 
doubt or cavil. 

Mr. Todd of Adelaide has recently obtained for his 
observatory a fine 8-inch telescope by Mr, Cooke. With 
this instrument, mounted in December, 1874, he has 
made many valuable observations of the motions of 
Jupiter's satellites. Ordinarily, of course, the entry of 
each satellite on the planet's face and the egress there- 
from, the disappearance of each satellite behind the 
planet or in the planet's shadow (not necessarily the 
same thing) and the reappearance^ are effected in what 



fHE PLAA^ET JUPITER. 21;^ 

fnay be called the normal way ; and Mr. Todd's experi- 
ence in this respect has been like 'that of other observers. 
But on two occasions he and his assistant, Mr. Ring- 
wood, observed that a satellite, when passing behind the 
planet's edge, did not disappear at once, but remained 
visible as if seen through the edge, for about tvro minutes. 
The same satellite behaved thus on each occasion, — viz. 
the satellite nearest the planet. As this satellite travels 
at the rate of about 645 miles per minute, it would follovr 
that the satellite was seen through a depth of nearly 
1300 miles, or, after making all possible allowance for 
optical illusions, some 900 or 1000 miles. The effect of 
refraction cannot then be great in the air of Jupiter, to 
this depth below the usual limit of the upper clouds, — 
for otherwise the satellite would have been altogether 
distorted. And this very fact, that for 1000 miles or 
so below the highest clouds the change of atmospheric 
density is not sufficient to produce any noticeable refrac- 
tive effects, implies that the true base of the atmosphere 
of Jupiter lies very far lower yet — -perhaps many hundreds 
of miles lower. 

If the reader now look again at the picture at page 201, 
he will understand, I think, how those great round white 
clouds in the chief belt,— clouds thousands of miles long 
and broad, — are probably hundreds of miles deep also, 
and float in an atmosphere still deeper. 



214 ^^^ PLANET JUPITER. 

All that we know about Jupiter, in fine, from direct 
observation, as well as all that we can infer respecting 
the past history of the solar system, tends to show that 
he is still an extremely young planet. He is the giant 
of the solar family in bulk, and probably he is far 
older than our earth in years; but in development he 
is, in all probability, the youngest of the sun's family 
of planets, and certainly far younger than the earth on 
which we live. 



XI 



THE RINGED PLANET SATURN 




ERY different from the ruddy planet which 
approached so closely to him in November, 
1877, is Saturn, the ringed world, thfe most 
wonderful of all the planets if the complexity of the 
system attending on him is considered, and in size 
inferior only to the giant Jupiter. 

It will have been noticed, perhaps, by those who are 
familiar with the aspect of the planets, that the contrast 
between Mars and Saturn during their late approach to 
us was not only greater than usual, but greater than was 
to be expected even when account was taken of the un- 
usual lustre of Mars. I have often wondered whether 
the ancient astronomers where ever perplexed by the 
varying lustre of Saturn. They recognised the fact that 
Mars has an orbit of great eccentricity (see the picture 
of the orbits of Mars, Venus, etc, at page 156) ; 



2i5 TllK RINGP.D PLANitT SAtVM!J<'. 

and there was nothing in the varying lustre of Mars 
v/hich could not be perfectly well explained by his 
known variations of distance, whether the Ptolemaic or 
the Copernican system were accepted. But with Saturn 
the case is different. His distance at successive returns 
to our midnight skies is subject to moderate changes 
only. Yet his brilliancy varies in a remarkable manner. 
We now know that those changes are due to the opening 
and closing of that marvellous system of rings which 
renders this planet the most beautiful of all the objects 
of telescopic observation which the heavens present to 
us. When the edge of the rings is turned towards 
the earth, we see only the most delicate thread of light 
on either side of the planet's disc. But when the rings 
are opened out to their full extent they reflect towards 
us as much light as we receive from the disc. At such 
times the planet presents a much more brilliant appear- 
ance than when the ring is turned nearly edgewise ; in 
fact to the naked eye he seems very nearly twice as 
bright. Now at present the rings are turned nearly 
edgewise towards the earth. In July and August; 1869, 
the planet presented in the telescope the appearance 
presented in {^g. 30, where it will be seen that the 
shorter axis of the oval into which any one of the ring- 
outlines is thrown is nearly equal to half the larger axis. 
Since then the rings have been slowly closing up ; and 



The ringed planet satI;rS\ itr 

at present the rings are so little open that the corre- 
sponding shorter axis, if it could be directly seen, would 
appear to be about one-sixteenth only of the larger axis. 
The rings were turned exactly edgewise towards the sun 
at two in the afternoon, on St. Valentine's day, 1878, 
according to calculations which I made in 1864, and 




Fig. 30. — The planet Saturn in July and August, 1869. 

published in a table under the head " Passages of the 
Rings plane through the Sun between the years 1600 
and 2000,'' in my ire.^iise entitled "Saturn and its 
System." The Nauti:al Almanac for 1878, indeed 
makes the passage of the rings plane through the sun 
occur somewhat earlier, stating that at noon on Feb- 
ruary 14 the sun's centre would pass south of the ring's 



218 T}IE RINGED PLANET SATURN 

horizon by about one-fifth of its apparent diameter (as 
seen by us). But my own calculation took into account 
certain small details which, in matters of this sort, the 
Nautical Alma?iac computers neglect. After all, it mat- 
tered very little to terrestrial observers whether the sun's 
light passed from the northern to the southern side of the 
rings a few hours earlier or later : the moment when it 
passed could not possibly be observed, even if it had 
occurred during the night hours. In the present instance 
it occurred at midday, and unfortunately none of the 
interesting phenomena presented in powerful telescopes 
when the rings are turned edgewise to the sun or earth 
could be observed, for they occurred when Saturn and 
the sun were nearly in the same part of the heavens, 
and when the planet therefore was utterly lost in the 
splendour of the solar rays. 

But now let us briefly consider what is known or may 
be surmised respecting the noble planet which was so 
far outshone in November, 1877, by the comparatively 
minute orb of Mars. 

Saturn travels at a distance from the sun exceeding 
rather more than nine and a half times that of our own 
earth. The second figure of orbits (see page 157) 
shows the wide span of his orbit compared with the 
earth's, and yet it will be seen that the orbits of Uranus 
and Neptune, planets unknown to the ancients, are 



THE RINGED PLANET SATVR^. 219 

SO wide that the path of Saturn becomes in turn small 
by comparison. 

Saturn has a globe about 70,000 miles in diameter, 
where it bulges out at the equator ; but he is somewhat 
flattened at his poles, so that his polar diameter is about 
7000 miles less than the equatorial diameter. In volume 
he exceeds our earth about 700 times ; but in mass only 
about ninety times : for his mean density is but about 
-^ of the earth^s. In fact, if we could imagine an ocean 
of water wide enough and deep enough for the planets 
to be all set in it, Saturn would float with about one- 
fourth of his bulk out of water, — always supposing that 
no change took place in his density directly after he was 
immersed. Saturn, indeed, would float highest of all the 
planets, or rather all of them would sink except Saturn 
and Neptune, and Saturn would float higher than Nep- 
tune. Uranus would just sink. Jupiter is half as heavy 
again as he should be to float. All the terrestrial planets, 
Mercury, Venus, the Earth, and Mars, would go to the 
bottom at once. 

It is almost impossible to regard any feature of Saturn 
as better deserving to be considered first than his ring 
system. Yet for the sake of preserving a due sequence 
of ideas we must first consider his globe. 

We find ourselves at once in presence of difficulties 
Uke those we encountered when we considered the planet 



250 "THE RINGED PLANET SATVrM. 

Jupiter. How is it that the mighty mass of a planet 
like Saturn, constructed, we have every reason to believe, 
of materials resembling those which constitute our earth, 
has so failed to gather in its substance that the mean 
density is much less than that of the earth's globe ? It 
must be remembered that gravity prevails throughout 
the frame of Saturn as throughout our earth's frame. 
Every particle of that enormous globe is drawn towards 
the centre with a force almost exactly the same as would 
be exerted by the attraction of the entire mass of that 
portion of the planet which lies nearer to the centre than 
the particle, if this mass were collected at the centre. 
But this is not all. It is not merely the attraction exerted 
on each particle of Saturn's mass which has to be con- 
sidered, bat the entire weight of all the superincumbent 
matter. The distinction between attraction and weight, 
by the way, is very commonly overlooked in considering 
the planets' interiors. I think it was Sir David Brewster 
who argued that as attraction can easily be shown to 
diminish downwards towards the centre, it is possible to 
conceive that the interior of a planet may be hollow. 
The error is readily perceived, if we take a familiar 
instance where the attraction is the same yet the effect 
of pressure very much greater. (Without voyaging to 
the centre of the earth, which is troublesome, and cer- 
tainly not a familiar experience, we cannot reach places 



THE RINGED PLANET SATURN 221 

where the attraction of gravity is greatly less than at the 
surface.) Take a massive arch of brickwork : the bricks 
near the top are subject to the same attraction as those 
belonging to the foundation ; but the pressure to which 
the foundation bricks are exposed is very much greater 
than that affecting the upper bricks. So again with a 
deep sea : the particles at the bottom of such a sea are 
subject to no greater attraction than the particles near 
the top ; but we know that a strong hollow case of metal 
which near the top of such a sea would be scarcely 
pressed at all, and would suffer no change of shape, 
will be crushed perfectly flat under the tremendous 
pressure to which it will be exposed when sunk to the 
bottom. 

There is, in fact, no escape from the conclusion that 
the interior portions of a planet like Saturn or Jupiter, 
nay, even of a body like our earth or the moon, must be 
subject to tremendous pressure, a pressure exceeding 
many hundred-fold the greatest which we can obtain 
experimentally, and that under that enormous pressure 
the density of the materials composing those central 
parts must be increased. How is it then that Saturn is 
of much smaller density than the earth? I can imagine 
no other explanation at once so natural and so complete 
as this, that an intense heat pervading the entire frame 
of the planet enables it to resist the tremendous pressure 



222 THE RINGED PLANET SATURN, 

due to mere weight. The planet's mass is expanded by 
the heat ; large portions which at ordinary temperatures 
would be solid are liquified or even vaporised ; matters 
which are liquid on our earth are vaporised; and, in 
fine, the planet assumes (as seen from our distant station) 
the appearance of being very much larger than it really 
is. We measure not the true globe, which, for aught that 
is known, may be exceedingly dense, but the dimensions 
of cloud-layers floating high in the planet's atmosphere. 

In describing Jupiter, I cor^sidered the changes which 
have been noticed in that planet's outline, and observed 
that it is impossible adequately to explain the evidence, 
without assuming that the changes of outline are real. 
The outline is not that of a solid globe, however, but of 
cloud-layers surrounding such a globe, and probably at a 
great distance from its surface. 

In Saturn's case we have very singular evidence to the 
same purpose. It was observed by Sir W. Herschel in 
April, 1805, that Saturn occasionally appears distorted, 
as though bulging out in the latitudes midway between 
the pole and the equator of the planet. Fig. 3 1 represents 
the appearance of the planet so far as shape is concerned, 
but the ring was not, when Sir W. Herschel observed it, 
so narrow as it is shown in fig. 31. In fact the ring had 
been turned edgewise to the earth two years before ; and 
when Herschel noticed the abnormal appearance of 



THE RINGED PLANET SATURN. 223 

baturn, the rings had begun to open out, though then' 
outermost outline was still far within the regions of the 
planet which seemed to project as shown. Fig. 31 in fact 
represents Saturn as seen by Schroter in 1803, when, as 
he said, the planet did not seem to present a truly 




Fig. 31. — Saturn's square-shouldered aspect. 

spheroidal figure. Herschel tested his observations by 
using several telescopes of different dimensions, — ten, 
seven, twenty, and forty feet in length. In 181 8, when 
the rings were scarcely visible, Kitchener saw the planet 
as shown in fig. 31, or '^ square-shouldered,'' as some have 
called it. On one occasion the present Astronomer- 



224 THE RINGED PLANET SATURN. 

Royal saw the planet of that figure. In January, 1855, 
Coolidge, using the fine refractor of the Cambridge U.S. 
Observatory, noticed that the equatorial diameter was 
not the greatest ; on the 9th the planet seemed of its 
usual shape ; but on December 6, Coolidge writes, '' I 
cannot persuade myself that it is an optical illusion which 
makes the maximum diameter of the ball intersect the 
limb half-way between the northern edge of the equatorial 
belt, and the inner ellipse of the inner bright ring." 
This was at a time when the rings were nearly at their 
greatest opening ; s,o that, including Schroter's observa- 
tion, we have Saturn out of shape when his ring has 
presented every shape between that shown in fig. 30 and 
that shown in fig. 31. Again, in the report of the Green- 
wich Observatory for 1860-61, when the ring was nearly 
closed, it is stated that '' Saturn has sametimes appeared 
to assume the square-shouldered aspect.'' Lastly, the 
eminent observers, G. Bond and G. P. Eond, father and 
son, have seen Saturn abnormally shaped, flattened un- 
duly in the north polar regions in 1848, when the ring 
was turned edgewise towards us, and unsymmetrical in 
varying ways in 1855-57, when the ring was most 
widely opened. 

Yet the planet's outline is usually a perfect oval, and 
has been shown to be so by careful measurements effected 
in some instances by the same observers, who, making 



THE RINGED PLANET SATURN 225 

equally careful measurements, have found the planet to 
be distorted. 

Does it not seem abundantly clear that the great 
cloud-layers which float in the atmosphere of Saturn have 
a widely varying range in height, and that therefore as 
we see and measure the outline of the cloud-layers, we 
see and measure in effect a planet which is variable in 
figure? This seems so natural and complete an ex- 
planation of the observed peculiarities that it appears 
idle on the one hand to reject the evidence of some 
among the most skilful observers who have ever lived ; 
or, on the other, to imagine that the solid frame of 
the planet has undergone changes so tremendous as 
would be involved by the observed variations of outline 
if they really signified that a solid planet had changed 
in shape. 

The mighty globe of Saturn turns upon its axis nearly 
as quickly as Jupiter. It will be remembered that the 
Jovian day lasts only 9 J of our hours, and as the diameter 
of Jupiter is about ten times the earth's, the equatorial 
parts of the giant planet travel some twenty-six or twenty- 
seven times as fast as those of our own earth, which 
move (rotationally) at the rate of more than a thousand 
miles an hour. Saturn's equatorial parts do not move 
quite so fast, — in fact, in this respect, Jupiter comes first 

J5 



226 THE RINGED PLANET SATURN 

of all the members of the solar system, including the sun 
himself, Saturn's equatorial circuit being almost nine 
times the earth's, while his day is little more than five- 
twelfths of the earth's, it follows that his equatorial parts 
move twelve-fifths of nine times, or nearly twenty-two 
times faster than the earth's. Their actual rotational 
rate is rather more than 22,000 miles an hour, or 367 
miles a minute, or more than six miles a second. This 
is a wonderful rate of motion. It always seems to me 
one of the most striking results of modern astronomical 
research that we have to recognise in bodies like that dull 
looking star, — the heavy slow-moving Saturn, as the 
ancients called him,* — motions of such tremendous 
swiftness. The planet is not only rushing bodily along 
through space with a velocity of nearly six miles per 
second, but his equatorial parts are being carried round 
with a velocity somewhat exceeding six miles per second. 
(The coincidence must be regarded as accidental, but it 
has this curious effect, that the equatorial parts of Saturn 
near the middle of the disc we see are actually almost at 
rest with respect to the sun, being carried forward with 
the planet at the rate of about five miles and nine-tenths 
per second, and backward round the planet at the rate of 

* Who assigned to him, as his representative metal, lead — a metal 
'* heavy, dull, and slow,'* as Don Armado puts it, in ** Love's 
Labour Lost." 



THE RINGED PLANET SATURN, 227 

about six miles and one-tenth per second. In fact there 
are ahvays two points on the disc which are ahiiost 
exactly at rest with respect to the sun, viz., those two 
points north and south of the equator where the rota- 
tional velocity is about five miles and nine-tenths per 
second, the velocity of Saturn in his orbit. )'^ 

But let us turn from the contemplation of Saturn's 
globe, interesting though it undoubtedly is, to study 
those marvellous objects, the Saturnian rings. 

The history of their discovery is interesting, but 
must not here detain us long. Briefly, it runs as 
follows : — 

Galileo, in July, 16 10, observing the planet Saturn 
with a telescope not powerful enough to show the rings, 
imagined at first that Saturn had two companion planets, 
one on either side of him, as though helping the planet 
along upon his road. (From a table relating to the rings, 
in my treatise on " Saturn and its vSystem," the aspect of 
the ring, at the time of any such observation, can at once 
be inferred. In the present case, for example, it will be 
seen from the table that the rings were closing up as the 

* Attention has lately been called, by the astronomers of tlie 
Washington Observatoiy, to the fact that the statement usually 
made in our books of astronomy, that Sir W. Herscliel's late^ 
determination of Saturn's rotation period was loli. 29m., is incorrect. 
His only determination of the period gave loh. i6m. 44s. for the 
Saturnian day. 



228 THE RINGED PLANET SATURN 

time of their disappearance, December 28, 161 2, drew 
near.) A year and a half later, GaUleo looked again at 
Saturn, and lo ! the companion planets were gone. He 
was perplexed beyond measure. " What is to be said 
concerning so strange a metamorphosis?" he asked. 
** Are the two lesser stars consumed after the manner of 
the solar spots ? Have they vanished or suddenly fled ? 
Has Saturn, perhaps, devoured his own children? Or 
were the appearances indeed an illusion or fraud, with 
which the glasses have so long deceived me, as well as 
many others to whom I have shown them? Now, per- 
haps, is the time come to revive the well-nigh withered 
hopes of those who, guided by more profound contem- 
plations, have discovered the fallacy of the new obser- 
vations, and demonstrated the utter impossibility of their 
existence. I do not know what to say in a case so 
surprising, so unlooked for, and so novel. The short- 
ness of the time, the unexpected nature of the event, the 
weakness of my understanding, and the fear of being 
mistaken, have greatly confounded me." 

Hevelius was similarly perplexed by the constantly 
vayring appearance of the planet. "Saturn," he informed 
his contemporaries, " presents five various figures to the 
observer, to wit — first, the mono-spherical; secondly, 
the tri-spherical ; thirdly, the spherico-ansated ; fourthly, 
the elHptico-ansated ; fifthly, and finally, the spherico- 



TME kINCED PLAKEl" SATURr:. 259 

cuspidated ; " of which we can only say, like Mr. 
Gilbert's Ferdinando, that "we know it's very clever; 
but we do not understand it." 

It was not till 1659 that Huyghens, using a telescope 
forty yards long, was able to make out the real meaning 
of the appendages which had so perplexed Galileo and 
Hevelius. He announced to the world, in an anagram, 
his discovery that Saturn is girdled about by a flat ring 
nowhere touching the planet. 

Huyghens also discovered the largest of Saturn's 
moons. He looked for no more, having the idea that, 
since six planets and six moons were now known, no 
more moons existed. 

In 1663 the Brothers Ball discovered that the rings 
are divided into two, or, at any rate, that a broad black 
stripe, such as is shown in fig. 30, separates the outer 
portion of the ring from the inner. Two years later 
these observers saw the stripe on the northern side of 
the rings, when the rings had so shifted in position 
that observers saw their southern side. Dominic Cassini 
recognised a corresponding stripe on the southern side. 
This was regarded as proving that there is a real division 
between the rings. The width of the gap thus separating 
the outside of the inner ring from the inside of the outer 
cannot be less than 1,600 miles. 

Cassini also detected another Saturnian moon in 



1%Q THE klNGED PLANET SATUMM, 

October, 167 1, and, later, he discovered three others, 
making five Saturnian moons in all. 

Sir W. Herschel observed the rings with great care. 
He confirmed the discovery of the great division between 
the rings ; but rejected the idea which was beginning to 
be entertained in his time, that there are many divisions. 
He found reasons for suspecting, but never actually 
proved, that the outer ring turns round in about io| hours. 

He also detected two small moons close to the outer 
ring. One other moon, detected independently by Bond 
at the Harvard Observatory, Cambridge, U.S., and by 
Lassell in this country in 1848, completes the set of 
eight moons now knov/n to revolve around the planet 
Saturn. We need not here say much more about these 
moons, saving, perhaps, to note that the span of the 
entire Saturnian system of moons amounts to about 
4,400,000 miles, nearly double that of the Jovian system. 
This is the largest system of satellities known to us. It 
is wonderful to reflect, when we look at the dull, slow- 
moving Saturn, that not only is the planet itself 700 times 
larger than the earth, not only is it girdled about by a 
ring system having a span exceeding more than 20 times 
the diameter of this earth on which we live, but that 
the entire span of the system over which that distant 
planet rules exceeds more than eighteen-fold the distance 
separating our earth from the moon. 



i 



M . 



THE RINGED PLANET SATURN, 231 

Return we now, however, to the consideration of the 
Saturnian ring-system. 

In 1850 a singular discovery was made. It was found 
by Bond, in America, and, a few days later, independ- 
ently, by Dawes, in England, that inside the inner 
bright ring there is a dark ring almost as wide as the 
outer bright ring. One of the strangest circumstances 
about this inner ring is that where it crosses Saturn's disc 
the outUne of the planet can be distinctly traced through 
the dark ring, which is thus, in a sense, a semi-transpa- 
rent body. I say *4na sense," because it does not follow 
that it really consists of semi-transparent matter any more 
than it follows from our being able to see through a 
gauze veil that the individual threads forming the gauze 
are made of a semi-transparent material. 

On examining recorded observations of the planet 
evidence was found that this dark ring is not, as was at 
first supposed, a recent formation. Where it crosses 
Saturn it had been mistaken in former times for a 
dark belt. 

It had always been supposed that the rings are solid, 
or at any rate continuous bodies. The younger Cassini, 
indeed, ventured to express doubts on the subject, but 
with this solitary exception, no suspicion had ever existed 
among astronomers that the rings are otherwise than 
continuous, until the discovery of the dark ring. 



232 THE RINGED PLANET SATURN. 

When the singular fact was discovered that the body 
of the planet can be seen through the slate-coloured 
ring, the solidity of this ring, at any rate, began natur- 
ally to be questioned. The idea was suggested that 
this formation may be fluid. Mathematicians applied 
rigorous processes of investigation to the question 
whether a fluid ring can possibly exist in such a position. 
The inquiry led to a re-examination of the whole subject 
of the ring-system and its stability. Mathematicians 
took up the question where Laplace had left it more 
than half a century before. He had decided that solid 
rings might, under certain conditions, revolve around a 
planet without being broken. But his inquiry had not 
been carried to a conclusion. Now, when the work was 
completed, it was -found that the requisite conditions 
are certainly not fulfilled by the Saturnian ring-system. 
The rings should be situated eccentrically, and heavier 
at one side than the opposite. In fact they should have 
a perceptible " bias." They exhibit, on the contrary, the 
most perfect symmetry of figure — this. symmetry, indeed, 
constitutes the great charm of Saturn's telescopic appear- 
ance ; and although, occasionally, the ball has not seemed 
to be quite in the middle of the ring-system, the displace- 
ment has never approached that which theory requires. 

The conclusion to which mathematicians arrived was 
accordingly the following :— 



I 



THE RINGED PLANET SATURN. 233 

The rings may be held to be formed of a multitude of 
tiny satellites, travelling nearly in one plane, each pursu- 
ing its own course around Saturn, according to the laws 
of satellite motion, though of course disturbed by the 
attraction of its fellow-satellites. 

We owe this theory principally to the labours of 
Professor J. Clerk Maxwell, who gained the Adams Prize 
offered by the University of Cambridge for the best 
mathematical essay upon the conditions under which a 
ring-system such as Saturn's can exist. But Professor 
Pierce, of America, had (somewhat earlier) supplied a 
complete refutation of the idea that the rings are solid 
and continuous bodies. 

When the rings are fully open, as in fig. 30, the 
Saturnian system affords as charming an object for 
telescopic observation as the astronomer can desire. 
The rings are then exhibited in their full beauty. The 
divisions, the dark ring, and the strange shading of the 
middle ring, can be well seen in a telescope of adequate 
power. The telescopic view is still more interesting 
when (as in fig. 30) the planet throws a well-marked 
shadow upon the rings. 

But perhaps the most beautiful of all the features 
which Saturn presents to the telescopist is the strange 
variety of colour to be observed upon his surface, and 
upon that of the rings. Mr. Browning, the eminent 



234 '^^E RtMCED PLANET SATURN. 

optician, thus describes the colours which the planet 
presents in his 1 2-inch reflector : — 

**The colours I have used," he says, referring to a 
painting of the planet, ^^were — for the rings, yellow- 
ochre (shaded with the same) and sepia ; for the globe, 
yellow ochre and brown madder, orange and purple, 
shaded with sepia. The great division in the rings is 
coloured sepia" (not black as commonly described). 
" The pole and the narrow belts situated near it on the 
globe are pale cobalt blue." ^^ These tints," he. adds, 
are the nearest I could find to those seen on the planet ; 
but there is a muddiness about all terrestrial colours when 
compared with the colours of the objects seen in the 
heavens. These colours could not be represented in all 
their brilliancy and purity, unless we could dip our pencil 
in a rainbow, and transfer the prismatic tints to our 
paper." 

I can corroborate these remarks from observations 
made upon the planet with an 8|-inch reflector. It is, 
indeed, a circumstance worthy of note, that the colours 
of the planets are much more strikingly exhibited by 
reflecting telescopes than by refractors, insomuch that, 
while Sir W. Herschel and Messrs. De la Rue and 
Lassell, making use of the former class of instruments, 
have all recorded the marked impression which the 
colours of Saturn and Jupiter have made upon them, we 



THE RINGED PLANET SATl/RA, 235 

find that few corresponding observations have been 
made by observers who have been armed with even the 
most perfect specimens of the refracting telescope. 

It must be noticed, however, that the colours of Saturn 
and his ring-system can only be seen in the most favour- 
able observing weather. 



XII. 




FANCIED FIGURES AMONG THE STARS. 

THINK that every thoughtful student of the 
stars must have ^Yondered how the figures of 
the various objects now pictured in our star- 
maps came to be imagined in the heavens themselves. 
It is a convenient answer to inquiries of the sort to say 
that it became necessary at an early stage in the progress 
of astronomy to have some means of identifying and 
naming star-groups, and that the arrangement into con- 
stellations was as suitable as any other that could have 
been desired. But it seems to me altogether unlikely 
that, in the infancy of a science, a mere arbitrary arrange- 
ment, such as this explanation supposes, should have 
been adopted. If we try to imagine the position of the 
first observers of the stars, what they wanted, and what 
they were likely to do, — and this a priori method of 
dealing with such questions is, I believe, the only safe 



i 



FANCIED FIGURES AMONG THE STARS. 237 

one, — we perceive that the division of the stars into 
sets named after animals and other objects, without any 
real resemblance to suggest such nomenclature, is as 
unlikely a course as could possibly be conceived. Be- 
yond all question, I think, the first watchers of the skies 
(they can scarcely be called astronomers) would have 
taken advantage of imagined similarity, more or less 
close, between each remarkable group of stars and some 
known object, to identify the group, and to obtain a 
name by which to speak of it. 

Yet it must he admitted that, as the constellations are 
at present arranged and figured, it is very difficult, in the 
great majority of cases, to imagine the least resemblance 
between a constellation and the object from which it 
derives its name. This is not only true of the modern 
constellations, the preposterous pneumatic machines^ 
printing presses^ microscopes^ and so forth, with which 
Hevelius and his successors foolishly crowded the 
heavens. Even the oldest of the old constellations of 
Ptolemy, nay, some even of those which are found 
among all nations, present, according to their present 
configuration, scarce any resemblance to their antitypes. 
For instance, it is well known that the Great Bear was 
recognised by many nations besides the Greeks and those, 
whoever they may have been, from whom the Greeks 
derived the constellation. We learn that when America 



238 FANCIED FIGURES AMONG THE STARS, 

was discovered the Iroquois Indians called this con- 
stellation Okouari, or the Bear. So the inhabitants of 
Northern Asia, the Phoenicians, the Persians, and others, 
called this constellation the Bear. The Egyptians, not 
knowing the bear, called the constellation the Hippopot- 
amus, an animal resembling the bear in several respects, 
as in its heavy body, short inconspicuous tail, small 
head, and short ears. Yet the constellation, as at present 
figured, is certainly not in the remotest degree like a 
bear. Apart from the enormous tail given in the pictures 
to the bear (almost tailless in reality), it is impossible for 
the liveliest imagination to recognise a bear as the con- 
stellation is at present formed. Flammarion says that, 
" even if we take in the smaller stars that stand in the 
feet and head, no ingenuity can make it in this or any 
other way resemble a bear," adding the absurd explana- 
tion given by Aristotle, ^^ that the name is derived from 
the fact that of all human animals the bear was thought 
to be the only one that dared to venture into the frozen 
regions of the north, and tempt their soHtude and cold." 
As though the shepherds and tillers of the soil, who first 
gave names to the stars, were likely to consider such far- 
fetched reasons, even if they had known either the habits 
of the polar bears or had considered the relation of the 
northern star-groups to the polar regions of the earth. 
Now the question whether any real resemblance 



FANCIED FIGURES AMONG THE STARS, 239 

attracted the attention of the earlier observers in such 
cases as this is by no means without interest. If such 
a resemblance formerly existed, and docs not now exist, 
it would follow that quite a considerable proportion of 
the stars have changed in brightness. Considering that 
each star is a sun, the centre, most probably, of a system 
like that which circles around our own sun, such a con- 
clusion would be very startling indeed. It would have 
a special interest for ourselves, somewhat in the same 
way that the news that many railway accidents occur 
has an interest for those who travel much by rail. If 
accidents frequently happen to those other suns, in such 
sort that they either lose or gain greatly in brightness, an 
accident of one or other kind might well happen to our 
own sun, in which case the inhabitants of this earth 
would perish. For many of the stars, by our suppo- 
sition, would have changed so much as either to lose their 
character as the defining stars of a constellation or by 
accession of brightness to acquire that character which 
in old times they had not possessed. Now, assuredly, a 
change of brightness competent to affect our- sun's cha- 
racter (as viewed from any remote star system) in equal 
degree, would be destructive to the inhabitants of the 
earth. None at least of the higher races of animals or 
plants could bear the intense cold resulting from a change 
of the former kind, or the intense heat resulting from a 



240 FANCIED FIGURES AMONG THE STARS. 

change of the latter kind. Yet, if the constellations were 
once named because of their imagined resemblance to 
various objects, and if no such resemblance can now be 
even imagined, a change of one or other kind in the 
condition of our sun must be regarded as probable, — 
much in the same way that a regular traveller by train 
on any line must be regarded as exposed to danger, if 
accidents are known to be continually happening on that 
line. 

What I now propose to do is to inquire whether we 
may not find the true figures and proportions of the 
ancient constellations in another way — viz., not by 
looking for them among the constellations as at present 
bounded and figured in our star-maps, but by searching 
the heavens themselves for them. This general method 
of search occurred to me very long ago while I was 
preparing various star-atlases, but the special mode of 
illustration here adopted occurred to me lately, while 
preparing for young astronomers in the United States a 
series of monthly maps showing the skies towards the 
north, south, east, and west, at different times of the 
night all the year round, and in various latitudes within 
the limits of the States. When I was in America I 
noticed, as I travelled about over a tolerably wide range 
of latitude, that the varying attitlides assumed by several 
of the constellations suggested features of resemblance 



Pakcied figures amoa^ the stars, s^t 

to different objects. In constructing maps, simple in 
appearance, but based in reality on careful calculations, 
this characteristic came out more clearly. Adopting a 
particular way of presenting the connectiqu between the 
various stars of a constellation. I often found the figure 
suggested which liad actually been associated with the 
group of stars thus connected. Lastly, the idea of 
extending this method to other cases naturally occurred 
to me, and some of the results are presented in the 
present essay. 

The method of delineation referred to is simply that 
of connecting the stars of a group by lines, ad libiticm, 
that is, not merely introducing so many lines as will 
connect all the stars into a single set, but where necessary 
to complete the delineation of the imagined figure, 
adding other lines connecting pairs of stars belonging to 
the group, yet not sC many that every pair of stars Is con- 
nected by a line. The lines, again, need not be straight 
On the contrary, where a gi'oup of stars forms a stream, 
the natural way of joining them is by lines so curved as 
to follow the serpentine course thus suggested. And 
in other cases a slight curvature of the lines joining pairs 
of stars will seem permissible, because corresponding to 
a configuration suggested by the stars themselves. 

It is easily seen that in some of the simplest cases, the 
figure associated with a constellation is at once suggested 

t6 



242 PAXCIED FIGURES AMONG THE STARS, 

by this method of delineation. For instance, take the 
case of the Northern Crown. 

In this constellation we have a group which, while 
consisting of only a few stars, yet suggests very naturally 
the idea of a coronet of gems, as shown in fig. 2^2* The 
same is true also, though perhaps in less degree, of the 
Dolphin, as shown in fig. 33. It is noteworthy, by the 
way, that this constellation can hardly have been invented 
by landsmen. For though in our own time when the 
pictures of sea-creatures are accurately dnawn, so that 





Fig. 32. — The Xortheni Cio^v-a. 



Fig. 33. —The Dulphin. 



persons who have never been to sea may have a correct 
idea of tlie figure of such creatures, in old times it was 
exceedingly unlikely that any but sailors would have such 
familiar knowledge of the dolphin as to be reminded of 
that creature by a group of stars. 

A much more complex constellation than either of 
those just mentioned — the Scorpion, — is even better 
represented by lineation, as sho\NTi in fig 34. It is not, 
however, with cases so remarkable as these that the 



i 



FAKCIED FIGURES AMONG THE STARS. 243 

difficulty suggested at the outset is really connected. 
The instances of really remarkable resemblance are so 
few that they must be regarded as altogether exceptional. 
The best proof that the Scorpion is unmistakably 
pictured by the stars is to be found in the fact that the 




Fig. 34. — The Scorpion. 



modern map-makers have not in this case departed much 
from the older dehneations. No one, in fact, who knows 
what a Scorpion is like, could have any doubt as to 
the configuration of the body, at least, of the celestial 
Scorpion. So that though such a case illustrates well the 



244 PAKCIED figure."^ AMOl^G THE STA^S. 

way in which the method of delmealion I have suggested 
may be made to picture the object seen by the ancient 
observers in the heavens, it does not afford any answer 
to the difficulty indicated by those who assert that the 
Great Bear, the Lion, the Ship, and other of the old con- 
stellation figures, have no real existence among the stars. 
Before leaving the Scorpion, however, I must call 
attention to one or two points which this remarkable 
constellation seems to establish. First, it is clear that in 
Its case real resemblance suggested the association of a 
group of stars with a familiar object. Since this resenv 
blance remains, we infer that the group of stars presents 
now an appearance closely resembling that which it pre- 
sented four or five thousand years ago. And as there 
is no special reason why the stars of the Scorpion more 
than those of other constellations should retain their 
lustre unchanged, we gain a certain probability for the 
beUef that all the constellations are now very much as 
they were when first named. Indeed, it so happens that 
the region occupied by the Scorpion is perhaps that part 
of the heavens where changes would on the whole most 
probably occur, the region of the Milky Way crossed by 
the Scorpion being exceptionally irregular. We may 
note also that the part of the earth where the observers 
lived who called this constellation the Scorpion must 
have been one where the reptile is well known, a con- 



i 



\ 



FANCIED FIGURES AMONG THE STARS. 245 

elusion which seems to dispose of the belief that the 
first astronomers lived in high latitudes. 

Let us, now, however, take some of the more difficult 
cases. We cannot do better, perhaps, than take at the 
very outset the Great Bear, a constellation of which many 
astronomers have asserted that it no longer presents and 
probably never did present the slightest resemblance to a 
bear. 

I would lay down, in the first place, the hypothesis 
that the stars in the region of the heavens now occupied 
by the Great Bear must have reminded the earliest 
observers of a large, heavily-bodied, small-headed, short- 
eared, and short-tailed creature, such as either a bear or 
a hippopotamus. Next, it may be taken for granted that 
the creature of which they were thus reminded was one 
with which they were familiar ; and as we have already 
seen that the inventors of the oldest constellations cannot 
have lived in very high latitudes, we may conclude with 
great probability that the bear imagined in the heavens 
was not the Polar bear, but the bear from which the first 
shepherd astronomers had to defend their herds and flocks, 
— the Syrian bear, as it is commonly called, though the 
species inhabited also the greater part of Asia Minor in 
former times. The Indians may be supposed to have 
seen the grizzly bear, not the smaller black bear, in the 
heavens. The features to be looked for, then, among 



246 FANCIED FIGURES AMONG THE STARS. 

the stars, are those common to the bears of comparatively 
low latitudes — not those of the polar bear. 

So much premised we may proceed to inquire whether 
the region of the heavens occupied by the Great Bear 
presents such a creature with sufficient distinctness to 
suggest the idea of the animal to persons familiar with 
its aspect. 

It is perhaps hardly necessary to remark that we must 
not expect to find a complete far less a perfect picture 
of a bear, or lion, or ship, in a large region of the 
heavens such as is occupied by these constellations. 
If some characteristic feature of a bear could be 
recognised in a group of stars, the ancient observer 
would be content to recognise the region of the heavens 
which would be occupied by the entire figure of the 
animal, as belonging to a Great Bear, unless some 
marked peculiarity in the stars of that region abso- 
lutely prevented the most lively imagination from con- 
ceiving a bear's body there. As an instance of the 
latter kind may be mentioned the Bull and the Ship, 
both of which constellation figures are seen only in 
part. The Bull's head is exceedingly well marked, as is 
the stern of the ship xA.rgo, but the liveliest imagination 
cannot recognise the body and tail of a bull, or the 
fore-part of a ship, where these should be. Consequently 
the ancients always regarded the Bull as a half bull, 



FANCIED FIGURES AMONG THE STARS, 249 

and (as Aratus is careful to mention) they recognised 
only the stern of the good ship Argo. But in general, 
where only some marked feature of an object could 
be imagined, or perhaps two or three, they yet con- 
ceived the whole object to be shown in the heavens, 
though it may have been altogether impossible to 
distribute the other stars over the remaining portion 
of the object in such a way as to shov>^ any natural 
association. 

The Great Bear seems to have been a constellation of 
this sort. One can recognise the head of an animal like 
the bear or the hippopotamus, and also the feet of such a 
creature, but the proper disposal of the stars forming the 
animal's body is not so easy. This would not interfere, 
however, with the choice of the bear to represent the 
region of stars occupied by the constellation. Every one 
who has seen faces and figures in the fire — and who has 
not? — knows that one or two features will sufifice to 
suggest a resemblance ; either the imagination does all 
the rest, or else the idea is suggested that some other 
object partially conceals that portion of the imagined 
figure which is wanting. 

Fig. 35 shows how, as I conceive, a bear was figured in 
the heavens by those who, in various nations, gave to 
the stars of this part of the sky the name of the Great 
Bear. 



250 FANCIED FIGURES AMONG THE STARS, 

It will be noticed in the first place that the famous 
Septentriones (the seven stars of the Plough, as in England 
the set is called, the Dipper as it is called in America, 
the Corn-measurer as it was called by the ancient Chinese) 
has little or nothing to do with the configuration of the 
Bear, though forming a part of the constellation. It is 
the set of small stars forming the head which seems to 
have suggested the idea of a bear, though two of the 
paws are also well defined by the stars. But the out- 
lining of the head of a bear or hippopotamus is really 
sufficiently close to require no very lively imagination to 

fill it in. Fig. 36, giving these 
stars only, serves to show this,' 
I think. That the entire figure 
of a bear or hippopotamus was 
not recognised seems further 
shown by the figure assigned 
to the constellation in the 

Fig. 36. — The Bear's Head. 

Zodiac of Tentyra, or Den- 
derah, where it appears as in fig. 37. The smaller figure 
is supposed to represent the Little Bear. 

In the second place, the reader familiar with the con- 
stellations will perceive that several stars not at present 
appertaining to the Great Bear are included within the 
configuration itself of the animal in fig. 35. Thus the 
third magnitude star behind the right ear belongs tQ 



\ 




FANCIED FIGURES AMONG THE STARS. 251 

i 
the constellation of the Dragon ; the third magnitude star 

near the hind quarters is Cor Caroh*, the chief star of 

the modern constellation Canes Venatid, or the Hunting 

Dogs. Vi appears to me that we ought not to expect 

that the first observers of the heavens, in recognising 




f^'g- 37- — The constellations of the Bears, represented as a hippopotamus (?) 
and wolf (?) in the Dcndcrah Zodiac. 



imaginary features of resemblance between a group of 
stars and some known object, would be careful to inquire 
whether some among those stars were included in a 
group which they had compared or might afterwards 
compare with another object. It is very necessary for 



252 FANCIED FIGURES AMONG THE STARS. 

the astronomer of our time, nay, it may have even been 
very necessary for the astronomers of the times of Hip- 
parchus, Ptolemy, etc., to have the limits of the constel- 
lations clearly defined, and to let no conspicuous star 
be common to different constellations. But as regards 
the figures fancied in the heavens by the first observers 
of the stars, considerations of that sort would be of no 
importance whatever. Indeed, it is worthy of notice 
that even so late as the time of Bayer, who gave to the 
stars their Greek letters, the constellations were not 
separated from each other. He called the star now 
known as Beta Tauri only. Gamma Auriga aho^ so that 
now Auriga has stars Alpha, Beta, Delta, and so forth, 
but no Gamma. Similarly, we look in vain for any 
star Delta in the constellation Pegasus, simply because 
Bayer called one and the same star Alpha Andromedae 
and Delta Pegasi, the astronomers of our own time 
retaining only the former name for this star, — the bright 
one adorning the head of Andromeda. Even in our time 
it has been found impossible properly to separate 
the older constellations from each other, so that to 
this day the Scorpion remains entangled with the legs 
of Ophiuchus, who is further inextricably mixed up 
with the Serpent. In fact, the Serpent is divided into 
two separate parts by the body of Ophiuchus, map- 
makers having no choice but either to allow Ophiu» 



PAKCIED PlGUkES AMONG THE STARS. 255 

chus to divide the Serpent, or the Serpent to divide 
Ophiuchus. 

In the next case, that of the Great Lion, we have still 
further to depart from the modern configuration of the 
constellation. No one can imagine the remotest resem- 
blance between any part of a lion and the grouping of 
stars falling on the corresponding portion of Leo in the 
modern constellation. The nose of the Lion now falls 
near X (fig. 38); ^ and p forming the outline of the 
mane, ^ the end of the tail, e the nearer fore-paw, r the 
nearer hind-paw. The original Lion, I cannot doubt, 
was imagined somewhat as pictured in fig. '^'^, The 
head and mane are unmistakably pictured among the 
stars, the paws fairly, the relatively small quarters and 
the tufted tail exceedingly well — always remembering 
that anything like very close resemblance is not to be 
looked for between a widely extended group of stars 
and the figure of an animal or other large object. If 
we remember also that uncultured nations, like children, 
are much quicker in imagining resemblances than those 
carefully trained to recognise the artistic delineation of 
objects, we cannot be surprised to find that nearly all 
those nations who were acquainted with the lion imagined 
a large leonine figure in the part of the heavens now 
centrally occupied by our modern and most puny Lion^ 
but including portions of Cancer, the whole of Leo 



235 FAK'CIED FIGURES AMONG THE STARS. 

Minor (one of Hevelius's absurd inventions), the Hair of 
Berenice, and a star or two belonging to Virgo. 

We have to treat in a similar way the constellation 




Fig. 39- — The Original Ship " Argo." 



Argo of our present maps, to get the good ship Argo, as 
the ancients must have conceived the constellation. 
Fig. 39 shows the Ship as I imagine she was originally 
pictured. The stars which mark her curved poop belong 



FANCIED FIGURES AMONG THE STARS. 257 

in part at present (as doubtless they have long belonged) 
to the Larger Dog, while those which mark the steering- 
oar belong to the modern constellation Columba Noachi, 
-or Noah's Dove. It must be observed that the bright 
star Canopus, shown in the water, was not visible in the 
time of the first observers in the latitude where they 
probably dwelt. The mighty gyrating motion of the 
earth has caused these stars to be brought five or six 
degrees further from the southern pole of the heavens. 
But Canopus and a few of the small stars near it are 
the only stars which have thus been added to the con- 
stellation as seen from the regions inhabited by the first 
observers. (Canopus was known to the Arabian and 
Egyptian astronomers. ) 

This introduces another point which seems worth 
noticing. At present the ship Argo is never seen from 
any part of the earth's surface as pictured in fig. 39. 
When due south, the position whence in all northern 
latitudes the constellation is most favourably seen, the 
ship is always tilted up at the stern : one would say, in 
more nautical phrase, she is down by the head, if the 
ship had any fore-part ; but from time immemorial she 
has been a half-ship only. Some 4,000 years ago, how- 
ever, Argo stood nearly on an even keel when due south. 
Again, it is to the mighty gyrational motion of the 
earth that we have to look for the cause of the great 



258 FANCIED FIGURES AMONG THE STARS, 

change in the apparent position of the ship. The sphere 
of the fixed stars has remained all the time unchanged, 
or very nearly so, but the direction in which the earth's 
axis of rotation points has swayed round (much as the 
axis of a reeling top sways round) through about one- 
sixth part of a complete gyration. 

In the regions where astronomy first began as a science, 
Argo not only stood on an even keel but almost on the 
horizon when due south ; and the features of resemblance 
to a ship, which I have endeavoured to portray in fig. 39, 
must have seemed much more striking there (and then) 
than now. 

The fore-part of the ship, or rather that region of the 
heavens where the fore-part should be, is occupied by- 
great masses of the Milky Way in one of its brightest and 
most remarkable portions. I have sometimes fancied 
that in some of the old Zodiac temples of star^ worshippers 
the constellation Argo was depicted as a mighty ship, 
gemmed with stars, and heavily laden in its fore-part 
with great masses of gilded cloud to represent the 
Milky Way, and that from such representations of the 
constellation came the tradition of the ship Argo and 
its cargo of golden fleece. Many parts of the story of 
Jason and his companions seem to relate to objects 
depicted in the old constellation-domes, — as those relat- 
ing to the Dragon, to Hercules, Castor and Pollux, the 



^ 



FANCIED FIGURES AMONG THE STARS. 259 

Centaur, etc. There is also a curious reference, in the 
tradition, to the stern of the ship, which is much like 
what we can imagine as resulting from, an attempt to 
explain the appearance of this part only, in the set of 
constellation figures. We read that the entrance to the 
Euxine Sea was fabled to be closed up by certain rocks 
called Symplegades (the Clashers), which floated on the 
vrater, and when anything attempted to pass through 
came together w4th such velocity that not even birds 
could escape. Phineas advised them to let a bird fly 
through, and if the bird passed safely, to venture the 
passage. It passed with only the loss of its tail : and 
the Argo, favoured by Juno, and impelled by the utmost 
efforts of its heroic crew, passed also, though so narrowly 
that the meeting rocks carried away part of her stern- 
works, which remained fixed there thenceforward. 

For my own part, I think we may not only regard the 
story of the ship Argo as in reality a version, though 
much modified, of the account of Noah's deluge, but 
consider the series of constellations, Aquarius, Cetus, 
Eridanus, Argo, Corvus, Centaurus, Ara, and Sagittarius, 
as typifying the same narrative. It is somewhat curious 
that if we place these constellations in their original 
position, — that is, as they were before the changes which 
the earth's great gyration has introduced during the last 
four thousand years or so, — we find the following coin- 



26o FANCIED FIGURES AMONG THE STARS. 

c'idences with the account of the deluge. First comes 
Aquarius (whose beginning would correspond with the 
sun's position on or about the seventeenth day of the 
second month of the old Pleiades year) pouring water. 
His range on the ecliptic (or the space he occupies in 
the annual range represented in the zodiac temple) is 
about forty days. Then came the w^atery constellations 
Eridanus, the river; and Cetus, the sea monster, having, 
with the ship Argo, a range of about 150 days of the 
annual circuit. About forty days later in the circuit we 
had Corvus, the raven, whose feet rest on Hydra, the 
great celestial sea-serpent, as though no dry land could 
be found by the bird. A dove also, if we accept the in- 
terpretation above given of the Argo narrative, may have 
been represented in this part of the star temple. Next 
w^e have the Centaur, originally we know represented as 
a man only, offering an animal as sacrifice on the altar 
Ara. There is a cloud of stars rising from the altar : 
w^e may recall Manilius's account of the constellation, — 

*' Ara, ferens thuris, stellis imitantibus, ignem." * 



* *'The altar,- bearing fire of incense, pictured by stars." A re- 
markably bright and complex portion of the Milky Way lies near 
the constellation Ara, giving the appearance of smoke ascending 
from the altar, only the altar must be set upright, as in my Gnomon ic 
Atlas, not inverted as in all the modern maps. (It is shown pro- 
perly in the old Farnese globe). 



i 



FANCIED FIGURES AMONG THE STARS. 261 

In this cloud is the Bow of Sagittarius, the bow being 
originally alone shown, as it is indeed the only figure 
which can be imagined among the stars of this region. 
So that these constellation figures seem to typify Noah 
offering sacrifice on the Altar, and the Bow of Promise 
set in the cloud above the altar. It is curious, too, that 
' while the time of Noah's leaving the ark was a year and 
ten days from the beginning of the rains, the constel- 
lation Sagittarius overlaps the conjoined watery signs 
Capricornus and Aquarius (running south of them) by 
about so much as would correspond to ten days of the 
annual circuit of the heavens. 

The objections to the view of matters above indicated 
are, first, that the constellations referred to seem to have 
been formed because of real resemblance between the 
star-groups and the figures associated with them ; and, 
secondly, that the Zodiac temples were probably erected 
by star-worshippers, and would scarcely have been em- 
ployed to typify such a narrative as that of the Deluge. 
The theory that the narrative itself was an attempt to 
interpret pictures represented on a Zodiac temple will, of 
course, be objectionable to many readers ; though they 
may not be unwilling to believe that the fable of the 
Argonautic expedition had its origin in some such way. 

It will have been noticed that in the figures which I 



262 FANCIED FIGURES AMONG THE STARS. 

have given of the Great Bear^ Lion, and Ship, I have 
not altogether adhered to my idea of simply connecting 
the stars of a group by lines. To say the truth, although 
a rough notion of a bear, lion, or ship may thus be 
given, the figure so presented is not altogether satis- 
factory to the mind. In any case, as for instance even 
in the Scorpion (of all these figures the best marked), 
the line-figure is very imperfect. But in some cases it 
does suggest the idea of an animal or figure, or a part of 
either, much in the same way that the idea of a human 
figure can be suggested by a few lines forming a skele- 
ton figure, such as our old friend Tommy Traddles used 
to draw. Now the Lion, Bear, and Ship are not well 
suited for this sort of delineation, as anyone will find 
who tries to suggest the idea of a bear, lion, or ship (of 
the old-fashioned heavily-sterned sort) by means of a 
few lines. 

In order, however, to show that in some cases a 
skeleton figure can be formed by joining the stars of 
a constellation, and that the figure thus formed repre- 
sents (of course in an utterly inartistic sort of way) the 
object associated with those stars, I will now take one or 
two instances in which such resemblance suggested itself 
to me without being specially soiAght for. I might add 
to the Crown, Dolphin, and Scorpion, the Chair of 
Cassiopeia, the figure of Orion, and the constellation of 



FANCIED FIGURES AMONG THE STARS. 263 

the Cup; I omit these, however, not because they are 
unfit for my purpose, but because they so obviously 
illustrate my argument. No one, with the least power of 
imagination, can fail to see how a chair, a belted giant, 
and a cup, are pictured, as it were, in these constellations. 
I will take others where the resemblance is less obvious. 
Thus, I think scarcely anyone who is acquainted 
with the constellation Andromeda can have failed to be 
perplexed by the association of the figure of a chained 
lady with this group of stars. In the arrangement of 
the stars themselves, without lines drawn to connect 
them, no such figure can be imagined ; at least I fail 
utterly for my own part when I attempt to picture such 
a figure, even now that I recognise how the figure is 
formed, skeleton-wise, by connecting lines. I cannot but 
think this figure must have been imagined from pictures 
of the groups of stars with lines connecting them, and 
not from the stars themselves. There is this reason, 
among others, for so thinking, The lady's head is repre- 
sented by a single star, Alpherat. Now a single star in 
the sky, however bright, is not large enough to represent 
the head of a human figure like Andromeda's. But 
the representation of a bright star like Alpherat in a 
chart or sculpture has sufficient size to serve for a head, 
because size is the only way in which brightness can be 
indicated. 



264 FANCIED FIGURES AMONG THE STARS, 

In fig. 40 the stars forming the constellation Andro* 
meda are shown ; also the chair of Cassiopeia ; and, on 
the right, one of the fishes and the triangle. A group of 
stars in the upper left-hand corner marks the place of 




Fig. 40.— Aiidroixieila, 

the rock to which the chains are fastened which bind 
Andromeda's right hand. 

It cannot be said that the skeleton picture shewn 
in fig. 40 is very graceful or artistic ; but, on the other 



FANCIED FIGURES AMONG THE STARS. 265 

hand, it cannot, I think, be doubted that there is enough 
in it to suggest the idea of a chained person. The 
fish naturally suggests the idea that the place is by the 
sea-shore. And the chair suggests the idea of some one 
on the shore waiting and watching. In our own time^ 
probably, the idea suggested would be that of a person, 
taking a bath, while some one sat in a chair on the sands 
and waited for their turn. But to the old observers of 
the heavens, unfamiliar as they were with sea-side diver- 
sions, the notion would more naturally occur of a woman 
chained to a rock, 

Lifting her long \vhite arms, vlJespread, to the walls of the basalt ; 

while not far off was imagined among the stars the 
monster Cetus coming onward, 

bulky and black as a galley, 
Lazily coasting along, as the fish fled leaping before it. 

One of these fish is seen close by the figure of the chained 

Andromeda. Near at hand they imagined the father 

and mother of the lady ; Cassiopeia sitting close to the 

shore; but 

Cepheus far in the palace 
Sat in the midst of his hall, on his throne, like a shepherd of people,. 
Choking hif^woe diy-eyed, while the slaves wailed loudly around him. 

The story of Andromeda, as the reader doubtless 
knows, is not of Greek origin. Its real origin is lost in a 



266 FANCIED FIGURES AMONG THE STARS, 

far antiquit) . The Indians have the same story in their 
astronomical mythology, and almost the same names. 
Thus Wilford, in his Asiatic Researches, relating his 
conversation with an Indian astronomer, says, " I asked 
him to show me in the heavens the constellation of An- 
tarmada, and he immediately pointed to Andromeda, 
though I had not given him any information about it 
beforehand. He afterwards brought me a very rare and 
curious work in Sanscrit, which contained a chapter 
devoted to Upanachatras, or extra-zodiacal constellations, 
with drawings of Capuja (Cepheus), and of Casyapi 
{Cassiopeia), seated and holding a lotus flower in her 
hand ; of Antannada^ chained, with the fish beside her ; 
and last, of Parasiea (Perseus), who, according to the 
explanation of the book, held the head of a monster 
w^hich he had slain in combat; blood was dropping from 
it, and for hair it had snakes. '^ 

As another illustration of the method I have de- 
scribed, I give the constellation Pegasus, or, as it was 
sometimes called, the Half-horse. I do not assert that 
f'g. 41 presents a very well shaped steed, any more than 
that in fig. 40 a lady of exquisite proportions is pictured. 
But one can perceive how the stars suggest the idea of a 
horse in one case, and of a human figure with upraised 
fastened arms in the other. It is commonly stated that 
Pegasus is one of the constellations showing no resem- 



FANCIED FIGURES AMONG THE STARS, 267 

blaiice at all to the figure associated with it. I think 
fig. 41 suffices to show that there is some sHght resem- 
blance at least. 

It may be mentioned, in passing, that all the nations 
of antiquity would not be likely to form equally clear 




Fig. 41. — Pegasus. 

conceptions of figures in the heavens. There are 
marked differences between the various races of the 
human family in this respect, just as there are marked 
differences between various persons in the power of 
imagining figures under different conditions. Some 
persons see figures at once in a cloud, in the outline of a 



268 FANCIED FIGURES AMONG THE STARS. ^ 

tree, in a fire, in a group of accidental markings, and 
so forth : while others not only do not see such figures, 
but cannot imagine them even when their outlines are 
indicated. So it is with different races of men. There 
have been some which, even when only just emerging 
from the utterly savage state, possessed so much of the 
imaginative power as to be able to picture for themselves, 
by lines cut with rude flint instruments on pieces of bone, 
horn, or ivory, the animals with which they were familiar. 
We have even among such pictures some belonging to 
an age so remote that the mammoth (or hairy elephant) 
had not yet entirely disappeared from Europe; for, in 
the cave of La Madeleine, at Dordogne, among other 
relics of the stone age, there has actually been found a 
drawing of the mammoth scratched on a piece of mam- 
moth tusk. On the other hand, there are some races in 
existence at the present day, in a more advanced stage 
of civilization, who cannot perceive even in well-exe- 
cuted coloured drawings any resemblance to the objects 
pictured. An aboriginal New Hollander, says Oldfield, 
*^ being shown a coloured engraving" of a member of his 
own tribe, '^ declared it to be a ship, another a kangaroo, 
and so on ; not one of a dozen identifying the portrait as 
having any connection with himself" A rude drawing, 
with all the lesser parts much exaggerated, they can 
realise. Thus, to give them an idea of a man, the head 



4 



FANCIED FIGURES AMONG THE STARS. 269 

must be drawn disproportionately large. Dr. CoUing- 
wood tells us that when he showed a copy of the Illus- 
trated London News to the Kibalaus of Formosa, he found 
it impossible to interest them by pointing out the most 
striking illustrations, '' which they did not appear to 
comprehend." Denham (I quote throughout from Lub- 
bock's most \'aluable and interesting work on the Origin 
of Civilization) says that Bookhaloum, a man otherwise 
of considerable intelligence, though he readily recognised 
figures, could not understand a landscape. '^ I could 
not,'' he says, ^^make him understand the print of the 
sand-wind in the desert, which is really so well de- 
scribed by Captain Lyons' drawing. He would look at 
it upside down ; and when I twice reversed it for him he 
exclaimed, * Why ! why ! it's all the same.' A camel or 
a human figure was all I could make him understand, 
and at these he was all agitation and delight. ' Gieb ! 
Gieb ! — wonderful ! wonderful ! ' The eyes first took his 
attention, then the other features; at the sight of the 
sw^ord, he exclaimed, ' Allah ! Allah ! ' and, on discovering 
the guns, instantly exclaimed, ' Where is the powder ? ' " 
We have in the consideration of this diversity of 
character between different races and nations, as respects 
the power as well of imagining as of delineating figures 
(the two are closely connected), one means of judging 
to what race we owe the oridnal constellations. For 



270 FANCIED FIGURES AMONG THE STARS. 

although some figures in the heavens are manifest 
enough, others require a considerable power of imagina- 
tion. And it should be noted that this must have been 
true even if we suppose (which I think I have succeeded 
in showing we need not do) that many of the stars have 
changed in brightness, and that thus resemblances have 
disappeared which formerly existed. For, in any case, 
the heavens four, ten, or twenty thousand years ago, or 
at whatever remote period we set the original invention 
of the constellations, must have presented the same 
characteristics as at present. It can never have been the 
case that all the star-groups could be compared at once, 
obviously, with the figures of men and animals. So that 
only a race of lively imagination could have found figures 
for all the star-groups, as was certainly done in very 
remote times by some race. 

The race, then, to whom we owe the general system 
of constellations, was probably one with so much talent 
for artistic delineation that in later ages this people 
would have become distinguished for skill in painting and 
sculpture. I think the sculptures found in Babylon, and 
the traditions left of the artistic skill of the Babylonians, 
correspond well with the belief that the constellations 
had their origin, and astronomy its first development, 
among that people or a kindred race. 

But the chief lesson to be derived (and I think it may 



^ 



FANCIED FIGURES AMONG THE STARS. 271 

fairly be derived) from the study of the constellation- 
groups is, that enough resemblance still remains, if only 
the arbitrary boundaries invented for the constellation 
figures in recent times are overlooked, to assure us that 
no veiy great changes have taken place in the aspect of 
the heavens for thousands of years. A few stars here 
and there have certainly changed greatly in brightness, 
and some few have changed considerably even in 
position ; while a considerable number have probably 
changed slightly in brightness, and all, or very nearly 
all, have changed somewhat in position. But on the 
whole the aspect of the stellar heavens now is the 
same as it was when the constellation figures were first 
imagined. 

This thought not only assures us of the permanence 
of our own sun (seeing that among the thousands of 
his fellow-suns which spangle the heavens so few have 
changed in lustre), but seems to me to give to the study 
of the stars a singular charm. Our antiquaries and 
archaeologists present for our study the relics of long 
past ages, and we may often rest assured that the objects 
thus gathered for us were really used in old times, 
though probably in a manner not understood by us, and 
when in a condition very unlike that in which they have 
reached our times. In nearly all such instances, however, 
doubt exists as to the antiquity of the relic, as to the 



272 FANCIED FIGURES AMONG THE STARS, 

race to whom it really belonged, and as to its real use 
and purport. But as regards the stellar heavens we 
liave no doubt. Of all the objects on which the eyes of 
remote races have rested, the celestial bodies are un- 
doubtedly the most ancient, while at the same time they 
and they alone were most certainly contemplated by all 
mankind. From the very earliest ages, from the time 
when the child-man first turned his thoughts from mere 
animal wants to the wonders of nature, the stars, and the 
sun and moon and planets must have drawn to themselves 
the attention of all who had eyes to see even though 
they had no power to understand the glories of the star- 
depths. Men pictured among the stars the objects most 
familiar to them, the herds and flocks which they tended, 
the herdsman himself, the waggoner, the huntsman, the 
birds of the air, the beasts of the field, the fishes of the 
sea, the ship, the altar, the bow, the arrow, and, one may 
say, all that according to their knowledge existed in the 
heavens above, in the earth beneath, and in the waters 
under the earth. Imperfect and anomalous as these 
meanings are, in relation to modern astronomy, with its 
exact methods, elaborate instruments, and profound 
investigations into the meaning of all the phenomena of 
the heavens, they nevertheless retain their place, and are 
likely long to do so, in virtue of the hold which they took, 
in remote ages, on the imagination of mankind in general. 



XITI. 



TRAiWSITS OF VENUS, 




^S a transit of Venus, visible in this coun- 
try, occurs in December, 1882, my readers, 
although they may not care for an account of 
the mathematical relations involved in the observation 
and calculation of a transit, will probably be interested 
by a simple explanation of the reasons why transits of 
Venus are so important in astronomy. 

Of course it is known that a transit of Venus is the 
apparent passage of the planet across the face of the 
sun, when, in passing between the earth and sun, as she 
does about eight times in thirteen years, she chances to 
come so close to the imaginary line joining tlie centres 
of those bodies that, as seen from the earth, she appears 
to be upon the face of the sun. We may compare her 
to a dove circling round a dovecot, and coming once in 
each circuit between an observer and her house. If in 



274 TRANSITS OF VENUS. 

her circuit she flew now higher, now lower, or, in other 
words, if the plane of her path were somewhat aslant, 
she would appear to pass sometimes above the cot, 
and sometimes below it, but from time to time she 
would seem to fly right across it. So Venus, in cir- 
cuiting round the sun, appears sometimes, when she 
comes between us and the sun, to pass above his face, 
and sometimes to pass below it ; but occasionally passes 
right across it. In such a case she is said to transit the 
sun's disc, and the phenomenon is called a transit of 
Venus. She has a companion in these circuiting motions, 
the planet Mercury, though this planet travels much 
nearer to the sun. It is as though, while a dove were 
flying around a dovecot at a distance of several yards, 
a sparrow were circling round the cot at a little more 
than half the distance, flying a good deal more quickly. 
It will be understood that Mercury also crosses the face 
of the sun from time to time — in fact, a great deal oftener 
than Venus ; but, for a reason presently to be explained, 
the transits of Mercury are of no great importance in 
astronomy. One occurred in 1861, another in 1868; 
another in May, 1878; yet very little attention was 
paid to those events; and before the next transit of 
Venus, in 1882, there will be a transit of Mercury, in 
November, 1881 ; yet no arrangements have been made 
for observing Mercury in transit on these occasions; 



TRANSITS OF VENUS. 275 

whereas astronomers began to lay their plans for observ- 
ing the transit of Venus in 1882, as far back as 1857. 

The illustration which I have already used will serve 
excellently to show the general principles on which the 
value of a transit of Venus depends ; and as, for some 
inscrutable reasons, any statement in which Venus, the 
sun, and the earth are introduced, seems by many to be 
regarded as, of its very nature, too perplexing for anyone 
but the astronomer even to attempt to understand, my 
talk in the next few paragraphs shall be about a dove, a 
dovecot, and a window, whereby, perhaps, some may be 
tempted to master the essential points of the astronomical 
question who would be driven out of hearing if I spoke 
about planets and orbits, ascending nodes and descend- 
ing nodes, ingress and egress, and contacts internal and 
external. 

Suppose D, fig. 42, to be a dove flying between the 
window A B and the dovecot C c, and let us suppose 
that a person looking at the dove just over the bar A 
sees her apparently cross the cot at the level a, at 
the foot of one row of openings, while another person 
looking at the dove just over the bar B sees her cross 
the cot apparently at the level b, at the foot of the 
row of openings next above the row a. Now suppose 
that the observer does not know the distance or size of 
the cot, but that he does know in some way that the 



276 



TRANSITS OF VENUS, 



dove flies just midway between the window and the 
cot; then it is perfectly clear that the distance a ^ 
between the two rows of openings is exactly the same 
as the distance A B between the two windows-bars; so 
that our observers need only measure A B with a foot- 
rule to know the scale on which the dovecot is made. 
If A B is one foot, for instance, then a d is also one 
foot; and if the dovecot has three equal divisions^ 




as shown at the side, then C (T is exactly one yard 
in height. 

Thus we have here a case where two observers, with- 
out leaving their window, can tell the size of a distant 
object. 

And it is quite clear that wherever the dove may pass 
betw^e.en the window and tlie house, the observers will 



TRANSITS OF J^EXUS. 



277 



oe equally able to determine the size of the cot, if 
only they know the relative distances of the dove and 
•dovecot. 

Thus, if D ^ is twice as great as D A, as in fig. 43, 

lb"" 




Fig- 43- 



then ^ ^ is twice as great as A B, the length which the 
observers know ; and if D ^^ is only equal to half D A, 
as in fig. 44, then ^ ^ is only equal to half the known 



ji. — 




Fig. 44. 



length A B. In every possible case the length of a I? 
is known. Take one other case in which the proportion 
is not quite so simple : — Suppose that D ^ is greater 




than D A in the proportion of 18 to 7, as in fig. 45 ; 
then <^ ^ is greater than A B in the same proportion ; so 
that, for instance, if A B is a length of 7 inches, If a i:^ 
a lens^th of 18 inches. 



^TS transits of VENUS. 

We see from these simple cases how the actual size of a 
distant object can be learned by two observers who do 
not leave their room, so long only as they know the re- 
lative distances of that object and of another which comes; 
between it and them. We need not specially concern 
ourselves by inquiring how they could determine this 
last point : it is enough that it might become known 
to them in many ways. To mention only one. Sup- 
pose the sun was shining so as to throw the shadow 
of the dove on a uniformly paved court between the 
house and the dovecot, then it is easy to conceive 
how the position of the shadow on the uniform paving 
would enable the observers to determine (by count- 
ing rows) the relative distances of dove and dovecot. 

Now, Venus comes between the earth and sun pre- 
cisely as the dove in fig. 45 comes between the window 
A B and the dovecot b a. The relative distances are 
known exactly, and have been known for hundreds of 
years. They were first learned by direct observation ; 
Venus going round and round the sun, within the path 
of the earth, is seen now on one side (the eastern side) 
of the sun as an evening star, and now on the other side 
(the western side) as a morning star, and when she 
seems farthest away from the sun in direction E V (fig. 
46) in one case, or E z; in the other case, we know that 
the line E V or E v, as the case may be, must just touch 



TRANSITS OF VENUS. 



279 



her path ; and perceiving how far her place in the 
heavens is from the sun's place at those times, we know, 
in fact, the size of either angle S E V or S E e;, and, 
therefore, the shape of either triangle S E V or S E z;. 
But this amounts to saying that we know what pro- 




Fig. 46. 

portion S E bears to S V — that is, what proportion the 
distance of the earth bears to the distance of Venus. '^' 



* There is, however, a much more perfect way of determining 
this proportion, by applying the law which Kepler found to con- 
nect the distances of the planets from the sun with the times in 
which they complete the circuits of their orbits. The law is that, 
if we take any two planets, and write do\vn the numbers expressing 
their periods of circuit (say in days), and the numbers expressing 
their distances from the sun (say in miles) in the same order ; then 
if we multiply each number of the first pair into itself, and each 



2go TRANSITS OF VENUS. 

Tliis proportion has been found to be very nearly 
that of I GO to 72; so that when Venus is on a line 
between the earth and sun, her distances from these 
two bodies are as 28 to 72, or as 7 to 18. 

These distances are proportioned precisely then as 
D A to D (3J in fig. 45 ; and the very same reasoning 
which was true in the case of dove and dovecot is 
true when for the dove and dovecot we substitute Venus 
and the sun respectively, while for the two observers 
looking oat from a window we substitute two observers 

number of the second pair twice into itself, the four numbers thus 
obtained will be proportional ; that is to say, as the first is to the 
second, so will the third be to the fourth. Now, as every one 
knows who has worked sums in the rule of three, when any three 
are given out of four proportionals, the fourth can always be 
found ; but we know the periods of circuit both of the earth and 
Venus (365-2564 days and 2247008 days respectively) very exactly 
indeed, because they have traversed their orbits so many times since 
they began to be observed by astronomers. We can call the earth's 
distance loo, and then applying the rule just stated, we get Venus' 
distance relatively to the earth's. The reader who cares to work 
out this little sum will find no difficulty whatever — if at least he is 
able to extract the cube roots of any number. The proportion 
runs thus : — 

365*2564 X 365-2564 : 224-7008 X 224-7008 

^: 100 X 100 X loo: (Venus' distance cubed;) 

Work out this sum and we get for Venus' distance 72*333. The 
ratio of Venus* distance to the earth's is almost exactly expressed 
by the numbers 217 and 300. 



TRAySlTS OF VENUS. 2S1 

Stationed at two different parts of the earth. It makes 
no difference in the essential principles of the problem 
that in one case we have to deal with inches, and in 
the other with thousands of miles ; just as in speaking of 
fig. 45 we reasoned that if A B, the distance between 
the eye-level of the two observers, is 7 inches, then 
^ ^ is 18 inches, so we say that if two stations, A and B, 
fig. 47, on the earth E, are 7000 miles apart (measuring 
the distance in a straight line), and an observer at A 






sees Venus' centre on the sun's disc at a, while an 
observer at B sees her centre on the sun's disc at b, 
then h a (measured in a straight line, and regarded 
as part of the upright diameter of the sun) is equal 
to 18,000 miles. So that if two observers, so placed, 
could observe Venus at the same instant, and note 
exactly where her centre seemed to fall, then since they 
would thus have learned what proportion ^ ^ is of 
the whole diameter S S' of the sun, they would know 
how many miles there are in that diameter. Suppose, 



282 TRANSITS OF VENUS. 

for instance, they found, on comparing notes, that b a 
is about the 47th part of the whole diameter, they 
would know that the diameter of the sun is about 47 
times 18,000 miles, or about 846,000 miles. 

Now, finding the real size of an object like the sun, 
whose apparent size w^e can so easily measure, is the 
same thing as finding his distance. Any one can tell 
how many times its own diameter the sun is removed 
from us. Take a circular disc an inch in diameter, 
— a halfpenny, for instance — and see how far away it 
must be placed to exactly hide the sun. The distance 
will be found to be rather more than 107 inches, so 
that the sun, like the halfpenny which hides his face, 
must be rather more than 107 times his own diameter 
from us. But 107 times 846,000 miles amounts to 
90,522,000 miles. This, therefore, if the imagined 
observations were correctly made, would be the sun's 
distance. 

I shall next show how Halley and DeHsle contrived 
two simple plans to avoid the manifest difficulty of carry- 
ing out in a direct manner the simultaneous observa- 
tions just described, from stations thousands of miles 
apart. 

We have seen that the determination of the sun's dis- 
tance by observing Venus on the sun's face would be a 
matter of perfect simplicity if we could be quite sure 



TRANSITS OF VENUS. 283 

that two observations were correctly made, and at exactly 
the same moment, by astronomers stationed one far to 
the north, the other far to the south. 

The former would see Venus as at A, fig. 48, the other 




would see her as at B ; and the distance between the 
two lines a d and h b\ along which her centre is travel- 
ling, as watched by these two observers, is known quite 
certainly to be i8,coo miles, if the observers' stations are 



284 TRANSITS OF VENUS. 

7,000 miles apart in a north-and-south direction (mea- 
sured in a straight line). Thence the diameter S S' of 
the sun is determined, because it is observed that the 
known distance a b \Sy such and such a part of it. And 
the real diameter in miles being known, the distance 
aiiust be 107 times as great, because the sun looks as 
large as any globe would look which is removed to a 
<iistance exceeding its own diameter (great or small) 
107 times. 

But unfortunately it is no easy matter to get the 
•distance a b, fig 48, determined in this simple manner. 
The distance 18,000 miles is known; but the difficulty 
is to determine what proportion the distance bears to 
the diameter of the sun S S'. All that we have heard 
about Halley's method and Delisle's method relates only 
to the contrivances devised by astronomers to get over 
this difficulty. It is manifest that the difficulty is very 
.great. 

For, first, the observers would be several thousand 
miles apart. How then are they to ensure that their 
observations shall be made simultaneously? Again, 
the distance a b h really a very minute quantity, and 
;a very slight mistake in observation would cause a very 
j2;reat mistake in the measurement of the sun's distance. 
Acordingly, Halley devised a plan by which one ob- 
.•ser\'er in the north (or as at A, ^xg. 47) would watch 



TRANSITS OF VENUS. 285 

Venus as she traversed the sun's face along a lower path^ 
as a a\ fig. 49 ; while another in the south (or as at B^ 
fig. 47) would watch her as she traversed a higher path^ 
as b h\ fig. 49. By timing her they could tell how long 




F'g. 49. 



these paths v\^ere, and therefore how placed on the sun's 
face, as in fig. 49 ; that is, how far apart, which is the 
same thing as determining/^ a, ^^g. 48. This was Halley's 
plan, and as it requires that the duration of the transit 



2S6 TRANSITS OF VENUS. 

should be timed, it is called the method of durations. 
Delisle proposed another method — viz., that one ob- 
server should time the exact moment when Venus, seen 
from one station, began to traverse the path a a!, while 
another should time the exact moment when she began 
to traverse the path b V ; this would show how much b 
is in advance of a, and thence the position of the two 
paths can be determined. Or two observers might note 
the end of the transit, thus finding how much d is in 
advance of b\ This is Delisle's method, and it has this 
advantage over Halley's — that an observer is only re- 
quired to see eitJier the beginning or the end of the 
transit, not both, 

I shall not here consider, except in a general way, the 
various astronomical conditions which affect the applica- 
tion of these two methods. Of course, all the time that 
a transit lasts, the earth is turning on her axis ; and as a 
transit may last as long as eight hours, and generally lasts 
from four to six hours, it is clear that the face of the 
earth turned towards the sun must change considerably 
between the beginning and end of a transit. So that 
Halley's method, which requires that the whole duration 
of a transit should be seen, is hampered with the diffi- 
culty arising from the fact that a station exceedingly well 
placed for observing the beginning of the transit might be 
very ill placed for observing the end, and vice versa. 



TRANSITS OF VENUS. 287 

Delisle's method is free from this objection, because an 
observer has only to note the beginning or the end, not 
both. But it is hampered by another. Two observers 
who employ Halley's method have each of them only to 
consider how long the passage of Venus over the sun's 
face lasts ; and they are so free from all occasion to 
know the exact time at which the transit begins and 
ends, that theoretically each observer might use such 
an instrument as a stop-watch, setting it going (right 
or wrong as to the time it showed) when the transit 
b^gan, and stopping it when the transit was over. But 
for Delisle's method this rough-and-ready method would 
not serve. The two observers have to compare the two 
moments at which they severally saw the transit begin, — 
and to do this, being many thousand miles apart, they 
must know the exact time. Suppose they each had a 
chronometer which had originally been set to Greenwich 
time, and which, being excellently constructed and care- 
fully watched, might be trusted to show exact Greenwich 
time, even though several months had elapsed since it 
was set. Then all the requirements of the method 
would be quite as well satisfied as those of the other 
method would be if the stop-watches just spoken of 
went at a perfectly true rate during the hours that the 
transit lasted. But it is one thing to construct a time- 
measure which will not lose or gain a few seconds in a 



288 



TRANSITS OF VENUS. 



few hours, and quite another to construct one which will 
not lose or gain a few seconds in a journey of many thou- 
sand miles, followed perhaps by two or three months' 
stay at the selected station. An error of five seconds 
would be perfectly fatal in applying Delisle's method, 
and no chronometer could be trusted under the condi- 



enas 




THE SUN 



i-''^g- 50. 



tions described to show true time within ten or twelve 
seconds. Hence astronomers had to provide for other 
methods of getting true time (say Greenwich time) than 
the use of chronometers ; and on the accuracy of these 
astronomical methods of getting true time depended 
the successful use of Delisle's method. 



TRAXSnS OF VENUS. 



289 



Then another difficulty had to be considered, which 
affected both methods. It was agreed by both Haliey 
and DeHsle that the proper moment to time the begin- 
ning or end of transit was the instant when Venus was 
just vt'ithin the sun's disc, as in fig. 50, either having just 




completed her entry, or being just about to begin to pass 
off the sun's face. If at this moment Venus presented a 
neatly defined round disc, exactly touching the edge of 
the sun, also neatly defined, this plan would be perfect. 
At the very instant when the contact ceased at the entry 
of Venus, the sun's light would break through between 

19 



290 TRANSITS OF VENUS. 

the edges of the two discs, and the observer would only 
have to note that instant ; while, when Venus was leaving 
the sun, he would only have to notice the instant when 
the fine thread of light was suddenly divided by a dark 
point. But unfortunately Venus does not behave in 




this way, at least not always. With a very powerful and 
very excellent telescope, in perfectly calm, clear weather, 
and with the sun high above the horizon, she probably 
behaves much as Halley and Delisle expected. But 
under less favourable conditions, she presents at the 
moment of entry or exit some such appearance as is 
shown in figures 51, 52, and SZ^ ^^'hile with a very low 



TJ^AmiTS OF VENUS. 291 

sun she assumes all sorts of shapes, continually chang- 
ing, being for one moment, perhaps, as in one or other 
of figs. 51, ^2, and 53, and in the next distorted into 
some such pleasing shape as is pictured in fig. 54. 

Accordingly, many astronomers are disposed to regard 




both Halley's method and Delisle's as obsolete, and to 
place reliance on the simple method of direct observation 
first described They would, however, of course bring to 
their aid all the ingenious devices of modern astronomical 
observation in order to overcome the difficulties inherent 
in that method. One of the contrivances naturally sug- 



292 



TRANSITS OF VENUS. 



gested to meet such difficulties is to photograph the sun 
with Venus upon his face. The American astronomers, 
in particular, consider that the photographic results 
obtained during the transit of 1874 will outweigh those 
obtained by all the other methods. The German and 




o 

Russfati kytfoAtif^ils^ & well as fiiose of Lord Lindsay's 
expedition, while placing great reliance on photography, 
^mg^loj^T^so^ a- uifthod of measuring the position of 
Venus on the s^n'^^sc,T)y means of a kind of telescope 
specially constructed for such work, the peculiarities of 
which need not be hoi"e considered. 



TRANSITS OF VENUS. 293 

The observations made in 1769 were so imperfect that 
astronomers deduced a distance fully 3,000,000 miles 
too great. Of late, other methods of observation had 
set them much nearer the true distance, which has been 
judged to lie certainly between 91,800,000 miles and 
92,600,000 miles — a tolerably wide range. 

But it may perhaps occur to some that the distance of 
the sun may be changing. The earth might be drawing 
steadily in towards the sun, and so all our measurements 
might be deceptive. Nay, the painful thought might 
present itself that when the observations of 1769 were 
made, the sun really was farther away than at present by 
more than 3,000,000 of miles. If this were so, the earth 
would, in the course of a century, have reduced her dis- 
tance by fully one-thirtieth part, so that, supposing the 
approach to continue, she would in 3,000 years fall into 
the sun, while, long before that period had elapsed, the 
increased heat to which she would be exposed would 
render life impossible. 

Fortunately, we know quite certainly that no such 
approach is taking place. It is known that the distance 
of the earth from the sun cannot change without a 
corresponding change in her period of revolution — that 
is, in the length of the year. The law connecting these 
two (indicated in the note, page 279) is such that, on the 
reduction of the distance by any moderate portion the 



294 TRANSITS OF VENUS. 

period would be reduced by a portion half as great again. 
For instance : if the distance of the earth from the sun 
were reduced by a thirtieth part (or about 3,000,000 
miles) the length of the year would be reduced by a 
thirtieth and half a thirtieth — that is, by a twentieth 
part, or by more than eighteen days. AVe know that no 
such change has taken place during the last century, or 
since the beginning of history. Nay, from the Chal- 
dean estimate of the length of the year, which only 
exceeded ours by about two minutes, it is easily shown 
that the distance of the earth from the sun has not 
diminished 200 miles within the last 2,500 years. So 
that, assuming even that the earth is approaching the 
sun at this rate, or eight miles in a century, it would be 
1,250,000 years before the distance would be diminished 
by 100,000 miles, which is the probable limit of error in 
the determination of the sun's distance. 

If, finally, it be asked, What, after all, is the use of 
determining the sun's distance ? the answer we shall give 
must depend on the answer given to the question. What, 
after all, is the use of knowing any facts in astronomy 
other than those useful in navigation, surveying, and so on? 
And I think that this question would introduce another 
and a wider one — viz., What is the use of that quality in 
man's nature which makes him seek after knowledge 
for its own sake ? I certainly do not propose to consider 



TRANSITS OF VENUS. 295 

this question, nor do I think that the reader will find 
any difficulty in understanding 7i>hy I do not. But 
accepting the facts : (i) that we are so constituted 
as to seek after knowledge ; and (2) that knowledge 
about the celestial orbs is interesting to us, quite 
apart from the use of such knowledge in navigation 
and surveying, it is easy to show that the determina- 
tion of the sun's distance is a matter full of interest. 
For on our estimate of the sun's distance depend our 
ideas as to the scale, not only of the solar system, 
but of the whole of the visible universe. The size of 
the sun, his mass, and therefore his might, the scale 
of those wonderful operations which we know to be 
taking place upon, and within, and around the sun ; 
all these relations, as well as our estimate of the size and 
mass of every planet, and therefore our estimate of the 
earth's relative importance in the solar system, depend 
absolutely and directly on the estimate we form of the 
sun's distance. Such being the case (this being in point 
of fact the cardinal problem of dimensional astronomy) it 
cannot but be thought that, great as were the trouble 
and expense of the expeditions sent out to observe 
the transit of 1874, they were devoted to an altogether 
worthy cause. 



Hazell, Watson, and Viney, Printers, London and Aylesbury. 



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